Top 100 Undisclosed Facts

These facts are 100 of the top board alerts. They summarize the concepts, principles, and most salient details of dermatologic pathology, diagnosis, and therapy.

1. Langerhans cells are antigen-presenting cells found in the epidermis; they are responsible for immune surveillance.


2. Apocrine glands, which are found in the highest concentration in the axillae and genital regions, produce odorless sweat that is acted on by bacteria to produce body odor.


3. Meissner corpuscles (touch) and Pacinian corpuscles (vibration) are the two primary encapsulated nerve receptors in the skin.


4. The Koebner phenomenon is produced by superficial trauma to the epidermis, causing certain preexisting skin diseases (e.g., psoriasis, lichen planus, lichen nitidus) to form at the site of trauma.


5. Lichen simplex chronicus is a secondary lesion consisting of a focal area of thickened skin with accentuated skin markings produced by chronic scratching or rubbing.


6. Maculopapular eruptions are most commonly seen with viral exanthems and drug-induced reactions.


7. In experienced hands, microscopic examination of KOH-treated clinical material (epidermal scale, hair, nails) is more sensitive than cultures for establishing the diagnosis of a dermatophyte infection.


8. Tzanck preparations are useful for quickly establishing the diagnosis of either varicella-zoster virus or herpes simplex virus infection but cannot distinguish between the two.


9. Nontreponemal test antibody titers (e.g., Venereal Disease Research Laboratory [VDRL]) are reported in the form of a titer and correlate with disease activity in syphilis. Adequately treated patients demonstrate low or negative titers. Treponemal tests (e.g., fluorescent treponemal antibody–absorption [FTA-ABS]) can be positive in both treated and untreated patients with syphilis. The test may revert to negative in some patients after treatment or remain positive indefinitely.


10. Topical emollients containing glycolic acid, lactic acid, urea, and glycerin are the mainstay of therapy in mild disorders of keratinization. In severe disorders of keratinization, oral retinoids are the most effective therapy.


11. Multiple Lisch nodules are pathognomonic of neurofibromatosis type 1 (NF-1). Multiple café-au-lait macules are the earliest skin sign of NF-1, occurring in approximately 80% of affected babies by the end of the first year of life. Neurofibromatosis type 2 most commonly presents with deafness or tinnitus related to underlying vestibular schwannomas.


12. Hypomelanotic macules are a useful diagnostic skin sign for tuberous sclerosis in infants with seizures.


13. Psoriasis classically has symmetrical red plaques with silver-white scale on elbows, and knees. Nail changes in psoriasis can mimic those seen with a dermatophyte fungal infection. Guttate psoriasis is more common in childhood than in later life.


14. Pityriasis rubra pilaris is characterized by large areas of orange-red–colored plaques with islands of sparing and thickened skin of the hands and feet.


15. Seborrheic dermatitis can be found not only on the scalp, but also on the face around the nares, on the central chest, in the axillae, and even on the genitalia.


16. Pityriasis rosea has oval papules and plaques that tend to arise along skin lines (“Christmas tree” pattern) with trailing scale (scale does not reach the end of the lesion).


17. The “two-pajama” treatment brings rapid relief to children with severe atopic dermatitis.


18. Eighty percent of contact dermatitis reactions are due to irritation, and 20% are due to allergic causes. Location of the dermatitis can help identify the causative agent. Patch testing is the only way to distinguish between allergic and irritant contact dermatitis.


19. Naproxen is the drug most commonly associated with pseudoporphyria. Vancomycin is the drug most commonly associated with drug-induced linear IgA bullous dermatosis.


20. Erythema toxicum neonatorum, a common pustular eruption of the neonate, is associated with peripheral eosinophilia in 20% of cases.


21. Cephalosporins are the most common drugs that produce generalized pustular drug eruptions (acute generalized exanthematous pustulosis).


22. The primary lesion of lichen planus is a flat-topped, pruritic, purple polygonal papule. Lichen planus may be clinically and histologically mimicked by numerous drugs (lichenoid drug eruptions).


23. In localized granuloma annulare, the lesions spontaneously resolve in 50% to 80% of patients within 2 years.


24. Rheumatoid nodules occur in 25% of patients with rheumatoid arthritis. Pseudorheumatoid nodules (deep granuloma annulare) most commonly occur as subcutaneous nodules in children and are not associated with rheumatoid arthritis.


25. Wegener’s granulomatosis is strongly associated (up to 90% of cases) with antibodies cytoplasmic antineutrophil cytoplasmic antibody (c-ANCA) directed against serine proteinase 3, an enzyme found in the cytoplasm of neutrophils. High titers correlate with increased disease activity.


26. The four primary functions of the skin are:
    1) barrier function and prevention of desiccation,
    2) immune surveillance,
    3) temperature control, and
    4) cutaneous sensation.


27. “Pinch purpura,” caused by amyloid deposition in blood vessel walls, is seen in systemic amyloidosis. Macroglossia may also be associated with systemic amyloidosis.


28. Thick plaques on the anterior shin in a patient with Graves’ disease is a typical finding in pretibial myxedema.


29. Calciphylaxis should be considered in the differential diagnosis of painful infarctive ulcerations in a patient with chronic renal failure.


30. In patients with erythropoietic protoporphyria, the red blood cells demonstrate fleeting fluorescence when examined with direct immunofluorescence. In patients with porphyria cutanea tarda, urine fluoresces a coral red color when examined under a Wood’s light.


31. Oculocutaneous albinism–1 (OCA-1) is due to inactive or missing melanocyte tyrosinase. It is characterized by a complete lack of cutaneous pigmentation, depigmented iris and retina, foveal hypoplasia, misrouted optic chiasm nerve fibers, and nystagmus.


32. Vitiligo is characterized by enlarging depigmented patches on the hands, elbows, and knees. Skin biopsy of a depigmented area reveals normal histology except for complete absence of epidermal melanocytes.


33. Tinea versicolor (TV) is characterized by hyper- or hypopigmented scaly patches on the chest and back. Microscopic analysis of lesional scales reveals multiple, short, blunt hyphae, and yeast. TV is due to overgrowth of normal flora, Pityrosporum (Malassezia globosa) yeast. It is often aggravated by heat and humidity.


34. Erythema ab igne is characterized by hyperpigmentation due to repeated heat exposure of the skin. No treatment is necessary as long as the patient stops using the heating pad. The hyperpigmentation will resolve in several months to a year.


35. Panniculitis is inflammation of the fat due to a wide variety of causes. Clinical clues, such as duration and location of the lesions, presence of ulcers, and association with systemic disease, can help in the initial evaluation. A deep incisional biopsy, including a wide base of fat, may be a critical evaluative tool.


36. Congenital ichthyosiform erythroderma and lamellar ichthyosis are the two disorders of keratinization that are most likely to present as a collodion baby.


37. In acne, the pilosebaceous unit is the target of disease. The microcomedone is the earliest lesion. Comedonal lesions should be treated with a topical retinoid. For inflammatory acne (red papules, pustules, or nodules), a topical or oral antibiotic should be used with a keratolytic and a benzoyl peroxide gel to minimize antibiotic resistance. Do not use antibiotics alone for acne vulgaris.


38. Perioral dermatitis is often caused by the inappropriate use of topical corticosteroids; always obtain a history of topical medication use.


39. Rosacea is common in fair-skinned caucasian adults. Reassure patients that treatment is available and that rhinophyma (W.C. Fields nose) is rare, especially in women. Fifty percent of rosacea patients will have some eye involvement; always obtain a history of eye symptoms and examine this area.


40. Dermatomyositis may present with normal muscle findings. This uncommon presentation is called amyopathic dermatomyositis or dermatomyositis sine myositis. Adult patients with dermatomyositis should have age-appropriate cancer screening, and women should be screened for ovarian carcinoma. Cancer screening is not necessary for pediatric-aged patients.


41. Acute urticaria is usually from a secondary cause such as an allergic reaction to food, drugs, insect stings, or infection. Chronic urticaria is most often idiopathic and not due to an allergic etiology but has an autoimmune basis in up to 50% of cases. The most common physical urticaria is dermographism, but in chronic urticaria, screen for physical stimuli such as pressure, cold, and heat.


42. For angioedema without urticaria, screen for both hereditary and acquired angioedema by obtaining a C4 level.


43. The STAR complex is a viral infection presenting as rash, pharyngitis, and monoarticular arthritis (sore throat, arthritis, and rash).


44. Parvovirus B19 is the cause of slapped cheeks (Fifth’s disease), and purpuric gloves and socks syndrome.


45. Most people with genital herpes do not know that they have it. Herpes simplex virus (HSV) infection may involve and recur at any location on the mucocutaneous surface.


46. Most human papillomavirus (HPV) infections are not carcinogenic, but persistent infections with some genotypes, especially HPV-16 and HPV-18, are associated with a high risk of epithelial neoplasia.


47. Epidermolysis bullosa is an inherited group of disorders characterized by genetic defects of structural proteins needed for the normal attachment and integrity of the epidermis.


48. The Jarisch-Herxheimer reaction is an acute febrile reaction, associated with shaking, chills, malaise, sore throat, myalgia, headache, and localized inflammation of infected mucocutaneous sites. It may occur 6 to 8 hours after penicillin treatment for infection, especially syphilis.


49. Leprosy is a chronic granulomatous infection caused by Mycobacterium leprae, affecting primarily skin and peripheral nerves. The nine-banded armadillo (Dasypus novemcinctus) carries Mycobacterium leprae and probably serves as the source of some cases of leprosy in Texas and parts of Louisiana.


50. Cutaneous tuberculosis has a broad clinical spectrum depending on the route of infection, virulence of the organism, and immune status of the host. Lupus vulgaris and scrofuloderma, although rare, are the two most common forms of cutaneous tuberculosis. M. tuberculosis can be diagnosed using acid-fast bacilli stains, culture, or polymerase chain reaction.


51. Deep fungal infections can be divided into subcutaneous (localized), systemic, and opportunistic categories. Localized fungal infections are due to local injury and implantation of the organism. Opportunistic fungal infections are increasingly common because of the rise in the number of organ transplant patients and human immunodeficiency virus (HIV) infection.


52. Creeping eruption (cutaneous larva migrans) occurs when the larvae of dog and cat hookworms (Ancylostoma caninum and A. braziliense) penetrate intact, exposed skin and begin migrating through the epidermis.


53. Attached ticks are best removed with traction, using blunt-angled forceps applied to the tick parts closest to the skin.


54. Patients with biopsy-proven Sweet’s syndrome should have a complete blood count to evaluate for an underlying hematologic malignancy.


55. Acanthosis nigricans is a common condition, and most cases are associated with obesity and insulin resistance.


56. Any refractory eczematous eruption on the breast should be biopsied to exclude mammary Paget’s disease. The diagnosis of extramammary Paget’s disease should prompt a careful evaluation for underlying gastrointestinal and genitourinary adenocarcinoma.


57. The presence of one or more xanthomas on the skin usually indicates an abnormality of lipid metabolism or, less commonly, a monoclonal gammopathy. The presence of eruptive xanthomas always indicates high levels of triglycerides. Patients with eruptive xanthomas are at increased risk to develop pancreatitis.


58. Bilirubin has a strong affinity for elastic-rich tissue, which accounts for its preferential accumulation in the sclera of the eyes.


59. Pyoderma gangrenosum is strongly associated with Crohn’s disease and ulcerative colitis. Surgical intervention in active pyoderma gangrenosum is contraindicated because it may produce extension of the ulcer.


60. Uremic frost is the presence of white deposits in the head and neck area in patients with severe renal failure. The pruritus of renal failure often responds to ultraviolet light B (UVB) therapy.


61. Small vascular lesions called angiokeratoma corporis diffusum are typically found in a bathing suit distribution in Fabry’s disease.


62. Nephrogenic fibrosing dermopathy is a recently described disease characterized by papules, plaques, and thickened skin of the trunk and extremities. It is associated with impaired renal function from many different causes.


63. Papulosquamous eruptions are defined by an inflammatory reaction consisting of red or purple papules or plaques with scale.


64. Oral hairy leukoplakia is a manifestation of Epstein-Barr virus infection.


65. Pellagra (due to deficiency of niacin and/or nicotinic acid) is most common in patients with corn-rich diets, alcoholism, gastrointestinal (GI) disease, carcinoid, and some drugs. The four classic symptoms start with the letter D: diarrhea, dermatitis, dementia, death. Casal’s necklace is the distinctive photosensitive eruption that presents around the neck.


66. Malignancy in a small congenital melanocytic nevus does not occur before puberty and overall is minimal.


67. Capillary hemangiomas are the most common vascular tumor of childhood.


68. Pyogenic granulomas are neither pyogenic nor granulomatous; they are neovascularizations, presenting as acute-onset, friable vascular papules that bleed frequently.


69. Direct immunofluorescence of perilesional skin is required in many cases to rule in or exclude the diagnosis of an autoimmune bullous disorder.


70. The majority of nonmelanoma skin cancers are on the face. One half are on the nose.


71. Breslow depth measurement levels are more accurate prognostic indicators than Clark’s level in malignant melanomas. The presence of in-transit metastases or satellite lesions indicates a worse prognosis than limited nodal metastases. There is currently no effective single-agent therapy for advanced melanoma.


72. Mycosis fungoides is a low-grade T-cell lymphoma with a median survival of 12 years for patients with patch or plaque stage disease. Management of mycosis fungoides is best accomplished by the involvement of several specialties, such as dermatology, dermatopathology/pathology, hematology/oncology, and radiation oncology.


73. Angiosarcoma, characterized as an erythematous or hemorrhagic macule or plaque, presents in three clinical settings: on the face and scalp of the elderly, in the setting of chronic lymphedema (Stewart-Treves syndrome), and in previously irradiated tissue.


74. Merkel cell carcinoma has a characteristic paranuclear “dot” that stains with cytokeratin but may be confused histologically with oat-cell carcinoma of the lung, malignant lymphoma, sweat gland carcinoma, metastatic carcinoid tumors, and Ewing’s sarcoma.


75. Microcystic adnexal carcinoma recurs frequently due to perineural invasion and classically presents on the upper lip (although it may be seen elsewhere on the face and beyond).


76. Dermatofibrosarcoma protuberans stains positively for the human hematopoietic progenitor cell antigen CD-34 and is histologically characterized by intersecting bundles of spindle-shaped cells with a characteristic storiform (cartwheel) arrangement.


77. Approximately 9% of all patients who die from internal malignancy will demonstrate metastatic tumors in the skin. Sister Mary Joseph’s nodule is the name applied to metastatic tumor in the umbilicus. It is most commonly seen in intraabdominal malignancies and is a poor prognostic sign.


78. Physicians should teach patients two basic concepts about skin cancer prevention: sun protection and self-examination of skin.


79. Phototoxic reactions clinically and symptomatically resemble sunburn, while photoallergic reactions resemble dermatitis.


80. The safe total maximum dose of 1% lidocaine for adults is 7 mg/kg, if combined with epinephrine, and 4.5 mg/kg, if given without epinephrine. The earliest signs of lidocaine toxicity include talkativeness, tinnitus, metallic taste, lightheadedness, diplopia, and circumoral pallor.


81. Buffering an anesthetic solution with 8.4% sodium bicarbonate in order to diminish the pain of injection will also shorten its duration of action.


82. Suture size does not correspond to a specific diameter, but rather to a specific tensile strength.


83. Pigmentation is determined by the type of melanin synthesized and the amount distributed to the surrounding keratinocytes.


84. Mohs micrographic surgery utilizes frozen sections of fresh tissue. It is indicated for tumor extirpation in zones of the face known to have high recurrence rates (e.g., nasolabial fold, nasal ala, medial canthus, pinna, postauricular sulcus). It offers cure rates of 99% for primary basal cell cancers and 95% for recurrent tumors.


85. Carbon dioxide and erbium:YAG lasers are used for tissue ablation.


86. Erythema nodosum is the most common cause of panniculitis.


87. Black tattoos are removed with the Q-switched 1064-nm Nd:YAG, the Q-switched alexandrite, and the Q-switched ruby lasers. Green tattoo pigment is removed only by the Q-switched alexandrite laser. Red tattoo pigment is removed only with the Q-switched 532-nm Nd:YAG laser.


88. PUVA is the acronym for psoralen plus ultraviolet light, type A.


89. Retinoids are structural analogs of vitamin A (retinol). Their most important functions include tissue differentiation (especially epithelial tissues), general growth, visual function, and reproduction. Systemic retinoids are potent teratogenic drugs.


90. The TORCHES infections are toxoplasmosis; other (varicella-zoster virus, parvovirus B19); rubella; cytomegalovirus; herpes simplex virus and HIV; enteroviruses and Epstein-Barr virus; and syphilis.


91. The three common causes of acquired circumscribed hair loss are alopecia areata, tinea capitis, and trichotillomania. A circular, scaly, or crusted bald spot on the scalp of a black child should be considered tinea capitis until proven otherwise. When a solitary lesion of alopecia areata is small, no treatment may be needed. The prognosis for such a lesion is excellent, and spontaneous regrowth often occurs.


92. Xerosis (dry skin, asteatosis, dermatitis hiemalis) is the most common geriatric dermatosis and the most common cause of pruritus in elderly patients.


93. Pruritic urticarial papules and plaques of pregnancy are the most common specific dermatosis of pregnancy.


94. Black skin manifests minor physiologic differences, including a stratum corneum with increased layers and cohesiveness and a decreased ability to synthesize vitamin D3.


95. Contact dermatitis is the most common form of occupational skin disease. Irritants cause 75% of occupationally induced contact dermatitis, while allergens are responsible for 25%. Treatment includes allergen and irritant avoidance, protective clothing, moisturizers, and topical steroids.


96. Gottron’s papules (erythematous to violaceous papules over the knuckles) are a cutaneous finding that is pathognomic of dermatomyositis.


97. Most viral exanthems are morbilliform.


98. The initial approach to the pruritic patient should focus on identifying and treating a primary skin disorder. If no obvious cause is found, look for evidence of systemic disease.


99. Bullous impetigo is always caused by Streptococcus aureus strains, usually phage II, type 71, that produce exfolliative toxins.


100. Syphilis is caused by the spirochete Treponema pallidum ssp. pallidum.