DERMATOLOGY BASICS

Dermatology is the branch of medicine dealing with the skin and its diseases,[1] a unique specialty with both medical and surgical aspects.[2][3][4] A dermatologist takes care of diseases, in the widest sense, and some cosmetic problems of the skin, scalp, hair, and nails.[3]
History of dermatology
Readily visible alterations of the skin surface have been recognized since the dawn of history, with some being treated, and some not.[citation needed] In 1801 the first great school of dermatology became a reality at the famous Hôpital Saint-Louis in Paris, while the first textbooks (Willan's, 1798–1808) and atlases (Alibert's, 1806–1814) appeared in print during the same period of time.[5] In 1952, Dermatology was greatly advanced by Dr. Norman Orentreich's pioneering work in hair transplantation.
[]Training

After earning a medical degree (M.D. or D.O.), the length of training in the United States for a general dermatologist to be eligible for Board Certification by the American Academy of Dermatology, is a total of four years. This training consists of an initial medical or surgical intern year followed by a three-year dermatology residency.[3][10][11] Following this training, one- or two- year post-residency fellowships are available in immunodermatology, phototherapy, laser medicine, Mohs micrographic surgery, cosmetic surgery or dermatopathology. For the past several years, dermatology residency positions in the United States have been one of the most competitive to obtain.[12][13][14]
[]Subspecialties

[]Cosmetic dermatology
Dermatologists have been leaders in the field of cosmetic surgery.[15] Some dermatologists complete fellowships in surgical dermatology. Many are trained in their residency on the use of botox, fillers, and laser surgery. Some dermatologists perform cosmetic procedures including liposuction, blepharoplasty, and face lifts.[16][17][18] Most dermatologists limit their cosmetic practice to minimally invasive procedures. Despite an absence of formal guidelines from the American Board of Dermatology, many cosmetic fellowships are offered in both surgery and laser medicine.[citation needed]
[]Dermatopathology
A dermatolopathologist is a pathologist or dermatologist who specializes in the pathology of the skin. This field is shared by dermatologists and pathologists. Usually a dermatologist or pathologist will complete one year of dermatopathology fellowship. This usually includes six months of general pathology, and six months of dermatopathology.[19] Alumni of both specialties can qualify as dermatopathologists. At the completion of a standard residency in dermatology, many dermatologists are also competent at dermatopathology. Some dermatopathologists qualify to sit for their examinations by completing a residency in dermatology and one in pathology.[20]
[]Immunodermatology
This field specializes in the treatment of immune-mediated skin diseases such as lupus, bullous pemphigoid, pemphigus vulgaris, and other immune-mediated skin disorders.[20][21] Specialists in this field often run their own immunopathology labs.[citation needed]
[]Mohs surgery
The dermatologic subspecialty called Mohs surgery focuses on the excision of skin cancers using a tissue-sparing technique that allows intraoperative assessment of 100% of the peripheral and deep tumor margins developed in the 1930s by Dr. Frederic E. Mohs. The procedure is defined as a type of CCPDMA processing. Physicians trained in this technique must be comfortable with both pathology and surgery, and dermatologists receive extensive training in both during their residency. Physicians who perform Mohs surgery can receive training in this specialized technique during their dermatology residency, but many will seek additional training either through preceptorships to join the American Society for Mohs Surgery[22] or through formal one- to two-year Mohs surgery fellowship training programs administered by the American College of Mohs Surgery.[23]
[]Pediatric dermatology
Physicians can qualify for this specialization by completing both a pediatric residency and a dermatology residency. Or they might elect to complete a post-residency fellowship.[24] This field encompasses the complex diseases of the neonates, hereditary skin diseases or genodermatoses, and the many difficulties of working with the pediatric population.[citation needed]
[]Teledermatology
Teledermatology is a form of dermatology where telecommunication technologies are used to exchange medical information via all kinds of media (audio, visual and also data communication, but typically photos of dermatologic conditions) usually made by non-dermatologists for evaluation off-site by dermatologists).[25][26] This subspecialty deals with options to view skin conditions over a large distance to provide knowledge exchange,[27] to establish second-opinion services for experts[28] or to use this for follow-up of individuals with chronic skin conditions.[29][30]
[]Therapies

Therapies provided by dermatologists include, but not restricted to:
Cosmetic filler injections
Hair removal with laser or other modalities
Hair transplantation – a cosmetic procedure practiced by many dermatologists.
Intralesional treatment – with steroid or chemotherapy.
Laser therapy – for both the management of birth marks, skin disorders (like vitiligo), Tattoo removal, and cosmetic resurfacing and rejuvenation.
Photodynamic therapy – for the treatment of skin cancer and precancerous growths.
Phototherapy – including the use of narrowband UVB, broadband UVB, psoralen and UVB.
Tattoo removal with laser.
Tumescent liposuction – liposuction was invented by a gynecologist. A dermatologist (Dr. Jeffrey A. Klein) adapted the procedure to local infusion of dilute anesthetic called tumescent liposuction. This method is now widely practiced by dermatologists, plastic surgeons and gynecologists.[31]
Cryosurgery – for the treatment of warts, skin cancers, and other dermatosis.
Radiation therapy – although rarely practiced by dermatologists, many dermatologist continue to provide radiation therapy in their office.
Vitiligo surgery – Including procedures like autologous melanocyte transplant, suction blister grafting and punch grafting.
Allergy testing – 'Patch testing' for contact dermatitis.
Systemic therapies – including antibiotics, immunomodulators, and novel injectable products.
Topical therapies – dermatologists have the best understanding of the numerous products and compounds used topically in medicine.
Most dermatologic pharmacology can be categorized based on the Anatomical Therapeutic Chemical Classification System, specifically the ATC code D.

Cutaneous conditions

A cutaneous condition is any medical condition that affects the integumentary system — the organ system that comprises the entire surface of the body and includes skin, hair, nails, and related muscle and glands.[1] The major function of this system is as a barrier against the external environment.[2]
Conditions of the human integumentary system constitute a broad spectrum of diseases, also known as dermatoses, as well as many nonpathologic states (like, in certain circumstances, melanonychia and racquet nails).[3][4] While only a small number of skin diseases account for most visits to the physician, thousands of skin conditions have been described.[5] Classification of these conditions often presents many nosological challenges, since underlying etiologies and pathogenetics are often not known.[6][7] Therefore, most current textbooks present a classification based on location (for example, conditions of the mucous membrane), morphology (chronic blistering conditions), etiology (skin conditions resulting from physical factors), and so on.[8][9]
Clinically, the diagnosis of any particular skin condition is made by gathering pertinent information regarding the presenting skin lesion(s), including the location (such as arms, head, legs), symptoms (pruritus, pain), duration (acute or chronic), arrangement (solitary, generalized, annular, linear), morphology (macules, papules, vesicles), and color (red, blue, brown, black, white, yellow).[10] The diagnosis of many conditions often also requires a skin biopsy which yields histologic information[11][12] that can be correlated with the clinical presentation and any laboratory data.[13][14]
Where cutaneous conditions occur
Integumentary system
The skin weighs an average of four kilograms, covers an area of two square meters, and is made of three distinct layers: the epidermis, dermis, and subcutaneous tissue.[1] There are two main types of human skin: glabrous skin, the nonhairy skin on the palms and soles (also referred to as the "palmoplantar" surfaces), and hair-bearing skin.[15] Within the latter type, there are hairs in structures called pilosebaceous units, each with hair follicle, sebaceous gland, and associated arrector pili muscle.[16] In the embryo, the epidermis, hair, and glands form from the ectoderm, which is chemically influenced by the underlying mesoderm that forms the dermis and subcutaneous tissues.[17][18][19]
[]Epidermis )
The epidermis is the most superficial layer of skin, a squamous epithelium with several strata: the stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, and stratum basale.[20] Nourishment is provided to these layers via diffusion from the dermis, since the epidermis is without direct blood supply. The epidermis contains four cell types: keratinocytes, melanocytes, Langerhans cells, and Merkel cells. Of these, keratinocytes are the major component, constituting roughly 95 percent of the epidermis.[15] This stratified squamous epithelium is maintained by cell division within the stratum basale, in which differentiating cells slowly displace outwards through the stratum spinosum to the stratum corneum, where cells are continually shed from the surface.[15] In normal skin, the rate of production equals the rate of loss; it takes about two weeks for a cell to migrate from the basal cell layer to the top of the granular cell layer, and an additional two weeks to cross the stratum corneum.[21]
[color=brown][]Dermis
The dermis is the layer of skin between the epidermis and subcutaneous tissue, and comprises two sections, the papillary dermis and the reticular dermis.[22] The superficial papillary dermis interdigitates with the overlying rete ridges of the epidermis, between which the two layers interact through the basement membrane zone.[22] Structural components of the dermis are collagen, elastic fibers, and extrafibrillar matrix (previously called ground substance).[22] Within these components are the pilosebaceous units, arrector pili muscles, and the eccrine and apocrine glands.[20] The dermis contains two vascular networks that run parallel to the skin surface—one superficial and one deep plexus—which are connected by vertical communicating vessels.[20][23] The function of blood vessels within the dermis is fourfold: to supply nutrition, to regulate temperature, to modulate inflammation, and to participate in wound healing.[24][25]
[color=brown][]Subcutaneous tissue
The subcutaneous tissue is a layer of fat between the dermis and underlying fascia.[5] This tissue may be further divided into two components, the actual fatty layer, or panniculus adiposus, and a deeper vestigial layer of muscle, the panniculus carnosus.[15] The main cellular component of this tissue is the adipocyte, or fat cell.[5] The structure of this tissue is composed of septal (i.e. linear strands) and lobular compartments, which differ in microscopic appearance.[20] Functionally, the subcutaneous fat insulates the body, absorbs trauma, and serves as a reserve energy source.[5]
Diseases of the skin include skin infections and skin neoplasms (including skin cancer).
Approach to diagnoses

The physical examination of the skin and its appendages, as well as the mucous membranes, forms the cornerstone of an accurate diagnosis of cutaneous conditions.[26] Most of these conditions present with cutaneous surface changes termed "lesions," which have more or less distinct characteristics.[27] Often proper examination will lead the physician to obtain appropriate historical information and/or laboratory tests that are able to confirm the diagnosis.[26] Upon examination, the important clinical observations are the (1) morphology, (2) configuration, and (3) distribution of the lesion(s).[26] With regard to morphology, the initial lesion that characterizes a condition is known as the "primary lesion," and identification of such a lesions is the most important aspect of the cutaneous examination.[27] Over time, these primary lesions may continue to develop or be modified by regression or trauma, producing "secondary lesions."[1] However, with that being stated, the lack of standardization of basic dermatologic terminology has been one of the principal barriers to successful communication among physicians in describing cutaneous findings.[20] Nevertheless, there are some commonly accepted terms used to describe the macroscopic morphology, configuration, and distribution of skin lesions, which are listed below.[27]
[]Morphology
[]Primary lesions

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Chigger bites on human skin showing characteristic welts

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Nodules


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Macule and patch

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Papule and plaque

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Vesicles and bulla

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Fissures, erosions and ulcers


Macule – A macule is a change in surface color, without elevation or depression and, therefore, nonpalpable, well or ill-defined,[28] variously sized, but generally considered less than either 5[28] or 10 mm in diameter at the widest point.[27]
Patch – A patch is a large macule equal to or greater than either 5 or 10 mm,[27] across depending on one's definition of a macule.[1] Patches may have some subtle surface change, such as a fine scale or wrinkling, but although the consistency of the surface is changed, the lesion itself is not palpable.[26]
Papule – A papule is a circumscribed, solid elevation of skin with no visible fluid, varying in size from a pinhead to less than either 5[28] or 10 mm in diameter at the widest point.[27]
Plaque – A plaque has been described as a broad papule, or confluence of papules equal to or greater than 1 cm,[27] or alternatively as an elevated, plateau-like lesion that is greater in its diameter than in its depth.[26]
Nodule – A nodule is morphologically similar to a papule, but is greater than either 5[26] or 10 mm in both width and depth, and most frequently centered in the dermis or subcutaneous fat.[27] The depth of involvement is what differentiates a nodule from a papule.[28]
Vesicle – A vesicle is a circumscribed, fluid-containing, epidermal elevation generally considered less than either 5[28] or 10 mm in diameter at the widest point.[27]
Bulla – A bulla is a large vesicle described as a rounded or irregularly shaped blister containing serous or seropurulent fluid, equal to or greater than either 5[28] or 10 mm,[27] depending on one's definition of a vesicle.[1]
Pustule – A pustule is a small elevation of the skin containing cloudy[26] or purulent material usually consisting of necrotic inflammatory cells.[27] These can be either white or red.
Cyst – A cyst is an epithelial-lined cavity containing liquid, semi-solid, or solid material.[28]
Erosion – An erosion is a discontinuity of the skin exhibiting incomplete loss of the epidermis,[29] a lesion that is moist, circumscribed, and usually depressed.[20]
Ulcer – An ulcer is a discontinuity of the skin exhibiting complete loss of the epidermis and often portions of the dermis and even subcutaneous fat.[29]
Fissure – A fissure is a crack in the skin that is usually narrow but deep.[26]
Wheal – A wheal is a rounded or flat-topped, pale red papule or plaque that is characteristically evanescent, disappearing within 24 to 48 hours.[28]
Telangiectasia – A telangiectasia represents an enlargement of superficial blood vessels to the point of being visible.[26]
Burrow – A burrow appears as a slightly elevated, grayish, tortuous line in the skin, and is caused by burrowing organisms.[26][27]

[]Secondary lesions
Scale – dry or greasy laminated masses of keratin[27] that represent thickened stratum corneum.[26]
Crust – dried serum, pus, or blood usually mixed with epithelial and sometimes bacterial debris.[28]
Lichenification – epidermal thickening characterized by visible and palpable thickening of the skin with accentuated skin markings.[1]
Excoriation – a punctate or linear abrasion produced by mechanical means (often scratching), usually involving only the epidermis but not uncommonly reaching the papillary dermis.[27]
Induration – dermal thickening causing the cutaneous surface to feel thicker and firmer.[26]
Atrophy – refers to a loss of tissue, and can be epidermal, dermal, or subcutaneous.[27] With epidermal atrophy, the skin appears thin, translucent, and wrinkled.[26] Dermal or subcutaneous atrophy is represented by depression of the skin.[26]
Maceration – softening and turning white of the skin due to being consistently wet.
Umbilication – formation of a depression at the top of a papule, vesicle, or pustule.
يتبع

تابع cutaneous conditions

Configuration

"Configuration" refers to how lesions are locally grouped ("organized"), which contrasts with how they are distributed

Agminate - in clusters
Annular or circinate - ring-shaped
Arciform or arcuate - arc-shaped
Digitate - with finger-like projections
Discoid or nummular - round or disc-shaped
Figurate - with a particular shape
Guttate - resembling drops
Gyrate - coiled or spiral-shaped
Herpetiform - resembling herpes
Linear
Mamillated - with rounded, breast-like projections
Reticular or reticulated - resembling a net
Serpiginous - with a wavy border
Stellate - star-shaped
Targetoid - resembling a bullseye
Verrucous - wart-like
Distribution
"Distribution" refers to how lesions are localized. They may be confined to a single area (a patch) or may exist in several places. Several distributions correlate an anatomical reference.[clarification needed] Some correlate with the means by which a given area becomes affected. For example, contact dermatitis correlates with locations where allergen has elicited an allergic immune response. Varicella zoster virus is known to recur (after its initial presentation as chicken pox) as herpes zoster ("shingles"). Chicken pox appears nearly everywhere on the body, but herpes zoster tends to follow one or two dermatomes; for example, the eruptions may appear along the bra line, on either or both sides of the patient.
Generalized
Symmetric - one side mirrors the other
Flexural - on the front of the fingers
Extensor - on the back of the fingers
Intertriginous - in an area where two skin areas may touch or rub together
Morbilliform - resembling measles
Palmoplantar - on the palm of the hand or bottom of the foot
Periorificial - around an orifice such as the mouth
Periungual - under a finger or toenail
Blaschkoid - following the path of Blaschko's lines in the skin
Photodistributed - in places where sunlight reaches
Zosteriform or dermatomal - associated with a particular nerve
Other related terms:
Collarette
Comedo
Confluent
Eczema (a type of dermatitis)
Granuloma
Livedo
Purpura
Erythema (redness)
Horn (a cell type)
Poikiloderma

Combined (conjoint) terms (maculopapular, papuloerosive, papulopustular, papulovesicular, papulosquamous, tuberoulcerative, vesiculobullous, vesiculopustular) are used to describe eruptions that evolve from one type of lesion to the next so often appear as having traits of both, when transitioning.
=

BASICS
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Varicella zoster virus (VZV) is one of eight herpes viruses known to infect humans and other vertebrates. It commonly causes chicken-pox in children and adults and Herpes zoster (shingles) in adults and rarely in children.
Primary VZV infection results in chickenpox (varicella), which may rarely result in complications including encephalitis or pneumonia. Even when clinical symptoms of chickenpox have resolved, VZV remains dormant in the nervous system of the infected person (virus latency), in the trigeminal and dorsal root ganglia.[1] In about 10–20% of cases, VZV reactivates later in life producing a disease known as shingles or herpes zoster. Serious complications of shingles include postherpetic neuralgia, zoster multiplex, myelitis, herpes ophthalmicus, or zoster sine herpete. Ramsay Hunt syndrome; VZV rarely effects the geniculate ganglion giving lesions that follow specific branches of the facial nerve. Symptoms may include painful blisters on the tongue and ear along with one sided facial weakness and hearing loss.
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Herpes zoster (or simply zoster), commonly known as shingles and also known as zona, is a viral disease characterized by a painful skin rash with blisters in a limited area on one side of the body, often in a stripe. The initial infection with varicella zoster virus (VZV) causes the acute (short-lived) illness chickenpox which generally occurs in children and young people. Once an episode of chickenpox has resolved, the virus is not eliminated from the body but can go on to cause shingles—an illness with very different symptoms—often many years after the initial infection. Herpes zoster is not the same disease as herpes simplex despite the name similarity (both the varicella zoster virus and herpes simplex virus belong to the same viral subfamily Alphaherpesvirinae).
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Chickenpox (or 'chicken pox') is a highly contagious illness caused by primary infection with varicella zoster virus (VZV).[1] It usually starts with vesicular skin rash mainly on the body and head rather than at the periphery and becomes itchy, raw pockmarks, which mostly heal without scarring. On examination, the observer typically finds lesions at various stages of healing.
Chickenpox is an airborne disease spread easily through coughing or sneezing of ill individuals or through direct contact with secretions from the rash. A person with chickenpox is infectious one to two days before the rash appears.[2] They remain contagious until all lesions have crusted over (this takes approximately six days).[3] Immunocompromised patients are contagious during the entire period as new lesions keep appearing. Crusted lesions are not contagious.[4]
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Blaschko's lines, also called the Lines of Blaschko, are skin lines invisible under normal conditions. They become apparent when some diseases of the skin or mucosa manifest themselves according to these patterns. They follow a "V" shape over the back, "S" shaped whorls over the chest, stomach, and sides, and wavy shapes on the head.[1]
The lines are believed to trace the migration of embryonic cells.[2][3] The stripes are a type of genetic mosaicism.[4] They do not correspond to nervous, muscular, or lymphatic systems. The lines can be observed in other animals such as cats and dogs.[5][6]
German dermatologist Alfred Blaschko is credited for the first demonstration of these lines in 1901


A blackhead (medically known as an open comedo,[1] plural comedones) is a yellow or blackish bump or plug on the skin, and usually found on the cheeks, nose, lip area, and chin. Blackheads are one of the common findings in acne vulgaris.[2] Contrary to the common belief that it is caused by poor hygiene, blackheads are caused by excess oils that have accumulated in the sebaceous gland's duct. The substance found in these bumps mostly consists of keratin and modified sebum (an oily secretion of the sebaceous gland), which darkens as it oxidizes. Clogged hair follicles, where blackheads often occur, reflect light irregularly to produce a blackhead's "black" hue.[3] For this reason, the blockage might not necessarily look black when extracted from the pore, but may have a more yellow-brown colour as a result of its melanin content.
In contrast, a "whitehead" (more commonly known as a pimple or a closed comedo) is a follicle that is filled with the same material, sebum, but lacks a small opening to the skin surface. Since the air cannot reach the follicle, the material is not oxidized, and remains white.[4]

Eczema or atopic dermatitis[2] (from Greek ἔκζεμα ēkzema, "to boil over") is a form of dermatitis,[3] or inflammation of the epidermis (the outer layer of the skin).[4]
The term eczema is broadly applied to a range of persistent skin conditions. These include dryness and recurring skin rashes that are characterized by one or more of these symptoms: redness, skin edema (swelling), itching and dryness, crusting, flaking, blistering, cracking, oozing, or bleeding. Areas of temporary skin discoloration may appear and are sometimes due to healed injuries. Scratching open a healing lesion may result in scarring and may enlarge the rash.
The word eczema comes from Greek words, that mean "to boil over". Dermatitis comes from the Greek word for skin – and both terms refer to exactly the same skin condition. In some languages, dermatitis and eczema are synonymous, while in other languages dermatitis implies an acute condition and "eczema" a chronic one.[5] The two conditions are often classified together.
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Granuloma is a medical term for a tiny collection of immune cells known as macrophages[1]. Granulomas form when the immune system attempts to wall off substances that it perceives as foreign but is unable to eliminate. Such substances include infectious organisms such as bacteria and fungi as well as other materials such as keratin and suture fragments.[2][3][4] A granuloma is therefore a special type of inflammation that can occur in a wide variety of diseases [1]. The adjective granulomatous means characterized by granulomas.
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Livedo refers to a form of skin discoloration.[1]

Purpura (from Latin: purpura, meaning "purple") is the appearance of red or purple discolorations on the skin that do not blanch on applying pressure. They are caused by bleeding underneath the skin. Purpura measure 0.3–1 cm (3–10 mm), whereas petechiae measure less than 3 mm, and ecchymoses greater than 1 cm.[1]
This is common with typhus and can be present with meningitis caused by meningococcal meningitis or septicaemia. In particular, meningococcus (Neisseria meningitidis), a Gram-negative diplococcus organism, releases endotoxin when it lyses. Endotoxin activates the Hageman factor (clotting factor XII), which causes disseminated intravascular coagulation (DIC). The DIC is what appears as a rash on the affected individual.
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Purpura are a common and nonspecific medical sign; however, the underlying mechanism commonly involves one of the following:
Platelet disorders (Thrombocytopenic purpura)
Primary thrombocytopenic purpura
Secondary thrombocytopenic purpura
Post-transfusion purpura
Vascular disorders (nonthrombocytopenic purpura)
Microvascular injury, as seen in senile (old age) purpura, when blood vessels are more easily damaged
Hypertensive states
Deficient vascular support
Vasculitis, as in the case of Henoch-Schönlein purpura
Coagulation disorders
Disseminated intravascular coagulation (DIC)
Scurvy (vitamin C deficiency) - defect in collagen synthesis due to lack of hydroxylation of procollagen results in weakened capillary walls and cells
Meningococcemia
Cocaine ingestion (according to a medical article by Francie Diep that appeared the September 2011 issue of Scientific American magazine, and Dr. Noah Craft, a dermatologist at Harbor-UCLA Medical Center, who co-authored the paper) if the one-time chemotherapy drug and now veterinary deworming agent levamisole is added by predominantly South American traffickers to cocaine because it dilutes, or cuts it, and supposedly makes it cheaper and prolongs the high, it can cause purpura of the ears, face, trunk, or extremities, sometimes needing reconstructive surgery.
There are also cases of psychogenic purpura described in the medical literature,[2] some claimed to be due to "autoerythrocyte sensitization". Other studies[3] suggest the local (cutaneous) activity of tPA can be increased in psychogenic purpura, leading to substantial amounts of localized plasmin activity, rapid degradation of fibrin clots, and resultant bleeding. Petechial rash is also characteristic of a rickettsial infection.

Erythema (from the Greek erythros, meaning red) is redness of the skin, caused by hyperemia of the capillaries in the lower layers of the skin. It occurs with any skin injury, infection, or inflammation.[1] Examples of erythema not associated with pathology include nervous blushes.[2]
Erythema (from the Greek erythros, meaning red) is redness of the skin, caused by hyperemia of the capillaries in the lower layers of the skin. It occurs with any skin injury, infection, or inflammation.[1] Examples of erythema not associated with pathology include nervous blushes.[2]
It can be caused by infection, massage, electrical treatment, acne medication, allergies, exercise, solar radiation (sunburn), cutaneous radiation syndrome, niacin administration [3], or waxing and tweezing of the hairs—any of which can cause the capillaries to dilate, resulting in redness. Erythema is a common side effect of radiotherapy treatment due to patient exposure to ionizing radiation.
In about 30–50% of cases, the cause of erythema is unknown.[citation needed]
Circumoral erythema has been described as a typical sign of acute oleander poisoning by ingestion.[1]
May also be caused by Vitamin A toxicity.[4]
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Poikiloderma is a skin condition that "consists of areas of increased and decreased pigmentation, prominent blood vessels, and thinning of the skin."[1]
Poikiloderma is most frequently seen on the chest or the neck, characterized by red colored pigment on the skin that is commonly associated with sun damage.

DERMATOLOGIC HISTOPATHOLOGY


Hyperkeratosis

Hyperkeratosis (from Ancient Greek: ὑπέρ (hyper, “over”); keratos - keratin) is thickening of the stratum corneum, often associated with a qualitative abnormality of the keratin,[1] and also usually accompanied by an increase in the granular layer. As the corneum layer normally varies greatly in thickness in different sites, some experience is needed to assess minor degrees of hyperkeratosis.
It can be caused by vitamin A deficiency or chronic exposure to arsenic.
It can be treated with urea-containing creams, which dissolve the intercellular matrix of the cells of the stratum corneum, promoting desquamation of scaly skin, eventually resulting in softening of hyperkeratotic areas.[2]
Types

[ Follicular
Follicular hyperkeratosis dass (also called "Phrynoderma") is a skin condition characterized by excessive development of keratin in hair follicles, resulting in rough, cone-shaped, elevated papules. The openings are often closed with a white plug of encrusted sebum.
This condition has been shown in several small-scale studies to respond well to supplementation with vitamins and fats rich in essential fatty acids. Some research suggests this is due mainly to E and B vitamins.[3] Vitamin A is also listed as connected to the pathology.[4]
[ ]By other specific site
Plantar hyperkeratosis is hyperkeratosis of the sole of the foot. It is recommended[5] to surgically remove the dead skin, to provide symptomatic relief.
Hyperkeratosis of the nipple and areola is an uncommon benign, asymptomatic, acquired condition of unknown pathogenesis.[6]:636
[ ]Hereditary
Epidermolytic hyperkeratosis (also known as "Bullous congenital ichthyosiform erythroderma,"[7] "Bullous ichthyosiform erythroderma,"[8]:482 or "bullous congenital ichthyosiform erythroderma Brocq"[9]) is a rare skin disease in the ichthyosis family affecting around 1 in 250,000 people. It involves the clumping of keratin filaments.[6]:562[10]
Multiple minute digitate hyperkeratosis, a rare cutaneous condition, with about half of cases being familial
Focal acral hyperkeratosis (also known as "Acrokeratoelastoidosis lichenoides,") is a late-onset keratoderma, inherited as an autosomal dominant condition, characterized by oval or polygonal crateriform papules developing along the border of the hands, feet, and wrists.[8]:509
[ Other
Hyperkeratosis lenticularis perstans (also known as "Flegel's disease"[7]) is a cutaneous condition characterized by rough, yellow-brown keratotic, flat-topped papules.[6]:639[7]

A keratin disease (or keratinopathy)
is a genetic disorder of one of the keratin genes.
An example is monilethrix.[1]
The first to be identified was epidermolysis bullosa simplex.
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OTHER histopathologies
Hyperkeratosis
Parakeratosis
Hypergranulosis
Acanthosis
Papillomatosis
Dyskeratosis
Acantholysis
Spongiosis
Hydropic swelling
Exocytosis
Vacuolization
Erosion
Ulceration
Lentiginou
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