Medical brain notes 15

  DISORDERS OF PIGMENTATION Vitiligo  causes irregular, completely depigmented skin patches. It is common andcan affect any race; there may also be a familial predisposition. The disease has an unknown etiology that is possibly autoimmune. Microscopically, affected areas are devoid of epidermal melanocytes. Melasma  causes irregular blotchy patches of hyperpigmentation on the face; it isassociated with sun exposure, oral contraceptive use, and pregnancy (“mask of preg-nancy”) and may regress after pregnancy. Freckles  (ephelides) are light brown macules on the face, shoulders, and chest. Theyare common in fair-skinned children and tend to darken and fade with the seasons due to sunlight exposure. Microscopically, freckles are characterized by increased melanin deposition in the basal cell layer of the epidermis with a normal number of melanocytes. Benign  lentigo  is a localized proliferation of melanocytes which cause small, oval, light brown macules. Micr...

  MELANOCYTIC TUMORS Congenital nevi  (birthmarks) are present at birth; giant congenital nevi haveincreased risk of developing melanoma. Nevocellular nevus  (mole) is a benign tumor of melanocytes (melanocytic nevuscells) that is clearly related to sun exposure. Types of nevi include junctional, compound, and intradermal. Nevi have uniform tan to brown color with sharp, well-circumscribed borders and tend to be stable in shape and size. Malignant trans-formation is uncommon. Dysplastic nevi  (BK moles) are larger and more irregular than common nevi, andthey may have pigment variation. Microscopically, the nevus exhibits cytological and architectural atypia. Dysplastic nevus syndrome is autosomal dominant ( CMM1  locus on chromosome 1); patients often have multiple dysplastic nevi; and there is increased risk of developing melanoma. Malignant melanoma  is a malignancy of melanocytes whose incidence is increasingat a rapid rate, with peak in ages 40–70. Risk...

  EPIDERMAL AND DERMAL LESIONS Acanthosis nigricans  causes thickened, hyperpigmented skin of the posterior neck,axillae, and groin; it is often associated with obesity and hyperinsulinism. On rare occasions it is associated with internal malignancy (stomach and other gastrointes-tinal malignancies). Seborrheic keratoses  are benign squamoproliferative neoplasms that are very com-mon in middle-aged and elderly individuals; they may occur on the trunk, head, neck, and the extremities. The lesions are tan to brown coin-shaped plaques that have a granular surface with a “stuck on” appearance, characterized microscopi-cally by basaloid epidermal hyperplasia and “horn cysts” (keratin-filled epidermal pseudocysts). They are usually left untreated, but may be removed if they become irritated or for cosmetic purposes. The sign of Leser-Trélat (paraneoplastic syn-drome) is the sudden development of multiple lesions which may accompany an internal malignancy. Psoriasis  is an ...

  MALIGNANT TUMORS Squamous cell carcinoma  (SCC) has peak incidence at age 60. Risk factors includechronic sun exposure (ultraviolet UVB); fair complexion; chronic skin ulcers or sinus tracts; long-term exposure to hydrocarbons, arsenic, burns, and radiation; immunosuppression; and xeroderma pigmentosum. Common mutations include  TP53  and  HRAS . ·              Precursors include actinic keratosis (a sun-induced dysplasia of the keratino-cytes that causes rough, red papules on the face, arms, and hands) and Bowen disease (squamous cell carcinoma  in situ ).   ·              Squamous cell carcinoma occurs on sun-exposed areas (face and hands) and causes a tan nodular mass which commonly ulcerates. Microscopic examina-tion shows nests of atypical keratinocytes that invade the dermis, (oftentimes) formation of keratin pearls, and inter...