Notes on Skin Disorders

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Viral disorders: warts:

• Human papillomavirus.

• Verrucous papular lesions.

Viral disorders: molluscum contagiosum:

• Caused by a poxvirus.

• Bowel-shaped lesions with keratin-filled central depression.

Viral disorders:

Rubeola (measles):

• RNA paramyxovirus.

• Prodrome, koplik spots, maculopapular rash.

Complications:

• Giant cell pneumonia, acute appendicitis, otitis media.

Rubella (German measles):

• RNA togavirus.

• 3-day measles.

• Painful lymphadenopathy.

• Findings: polyarthritis in adults.

Erythema infectiosum (fifth disease):

• Parvovirus B19 (DNA virus).

• Slapped face appearance; may extend to trunk.

Roseola infantum:

• Human herpesvirus 6 (DNA virus).

• Maculopapular rash, fever.

Varicella-zoster virus:

• DNA herpesvirus.

• Varicella (chickenpox): rash; + Tzanck test; Reye syndrome; pneumonia; cerebellitis.

• Herpes zoster (shingles).

Bacterial disorders:

S aureus:

• Toxic shock syndrome: fever, hypotension, sun-burn rash.

• Other: postsurgical infections, skin abscess, hidradenitis suppurativa.

Scarlet fever:

• S. pyogenes.

• Sandpaper-like rash; strawberry tongue.

Impetigo:

• S. aureus.

• Rash; honey-crusted, colored lesions.

Leprosy:

• M. leprae.

Tuberculoid type:

• Granulomas present; + lepromin skin test; nerve involvement.

Lepromatous type:

• No granulomas; foamy macrophages; Grenz zone; - lepromin test; leonine facies.

Acne vulgaris:

• Pilosebaceous unit inflamed.

• P. acnes.

• Two types: inflammatory (abnormal keratinization) and obstructive (blocked hair outlet).

Acne rosacea:

• Pilosebaceous units of face inflamed.

• Sebaceous gland hyperplasia.

Fungal disorders:

Superficial mycoses (dermatophytoses):

• Diagnosis: Wood's lamp and POH-treated skin scrapings.

Tinea capitis:

• Trichophyton tonsurans (- Wood's lamp).

• Microsporum canis (+ Wood's lamp); alopecia.

Tinea corporis:

• Trichophyton rubrum.

T. pedis

• Athletes foot.

T. crurus

• Jock itch.

T. unguium

• Nails.

T. versicolor:

• M. furfur.

• Not tanning white spots.

• KOH findings: spaghetti and meatballs.

Candida albicans:

Causes:

• intertrigo, onychomycosis.

Seborrheic dermatitis:

• M. furfur.

• Greasy dermatitis.

Sporotrichosis:

• S. schenckii.

• Traumatic implantation of fungus.

• Rose gardening.

Benign noninfectious disorders:

Ichthyosis vulgaris:

• Most common AD disorder.

• Defective keratinization causes increased thickness of skin.

Xerosis:

• Decreased skin lipids cause dry skin in elderly.

• Also causes: decreased sweat glands, decreased skin thickness.

Polymorphous light eruption:

• Common photodermatitis in native Americans.

Eczema:

• Inflammatory dermatoses.

• Acute: weeping, erythematous rash.

• Chronic: dry, thickened skin due to scratching.

• Atopic dermatitis: type I IgE-mediated hypersensitivity reaction in children.

• Contact dermatitis: allergic; type IV hypersensitivity reaction.

• Photodermatitis: UV light reaction.

Autoimmune disorders:

Chronic cutaneous lupus erythematous:

• Epidermal atrophy.

• DNA-anti-DNA immunocomplexes in basement membrane.

• Alopecia, + immunofluorescent band test.

• Butterfly rash; exacerbated by UV light.

Pemphigus vulgaris:

• IgG antibodies; type II hypersensitivity reaction.

• Positive Nikolsky sign.

Bullous pemphigoid:

• IgG antibodies against basement membrane.

• Type II hypersensitivity reaction.

• Negative Nikolsky sign.

Dermatitis herpetiformis:

• IgA-anti-IgA complex deposition.

Premalignant skin disorders:

• Actinic (solar) keratosis: prolonged UV light exposure.

• May give rise to squamous cell carcinoma.

Lichen planus:

• Association with hepatitis C.

• Pruritic, scaly, violaceous, flat-topped papules.

• Wickham's striae.

Psoriasis:

• Genetic predisposition.

• Undifferentiated proliferation of keratinocytes.

• Association with streptococcal pharyngitis.

• Koebner phenomenon: rash in areas of trauma.

• Plaques, pitting of nails.

• Munro microabscesses: neutrophils collect in stratum corneum.

Pityriasis rosea:

• Herald patch: plaque on trunk.

• Followed by rash in Christmas tree distribution.

Erythema multiforme:

• Hypersensitivity skin reaction to infection or drugs.

• M. pneumoniae; HSV.

• Stevens-Johnson syndrome.

Erythema nodosum:

• Lesion of fat; panniculitis.

• Association with bacterial and fungal infections.

Granuloma annulare:

• Dermal inflammation.

• Association with diabetes mellitus.

Porphyria cutanea tarda:

• Genetic or acquired.

• Deficiency of uroporphyrinogen decarboxylase.

• Wine-red urine, photosensitive bullous skin lesions, hyperpigmentation, fragile skin, increased lanugo.

Urticaria:

• Pruritic elevations of skin.

• Histamine release.

• Type I IgE-mediated reactions due to insect bites, foods, medications.

• Dermatographim: urticaria develops in areas of physical pressure.

Acanthosis nigricans:

• Verrucoid, pigmented skin lesion usually located in axilla.

Benign melanocytic disorders:

Solar lentigo:

• Elderly; increased melanocytes, brown liver spots.

Vitiligo:

• Autoimmune destruction of melanocytes; areas of depigmentation.

Chloasma:

• Seen in women taking contraceptive pills; hyperpigmented lesions on forehead and cheeks.

Neoplastic skin disorders:

Seborrheic keratosis:

• Individuals older than 50.

• Coin-like, stuck-on appearance; benign pigmented epidermal tumor.

• Leser-Trelat sign: increased number of keratoses.

Keratoacanthoma:

• Rapidly growing, benign crateriform tumor in sun-exposed areas.

Benign epidermal cysts:

• Epidermal inclusion cysts: derived from epidermis of hair follicle; located on face, base of ears, trunk.

• Pilar cyst: derived from hair root sheats; located on face and scalp.

Nevocellular nevus (mole):

• Benign tumor of neural crest-derived cells.

• Types: junctional (children and adolescents), intradermal (adults), and dysplastic nevi (may be associated with dysplastic nevus syndrome; may cause malignant melanoma).

Basal cell carcinoma:

• Due to chronic exposure to sunlight.

• Raised papule or nodule with central crater.

• Locally aggressive; does not metastasize.

Squamous cell carcinoma:

• Due to: UV, actinic (solar) keratosis, arsenic exposure, scar tissue in third-degree burn, orifice of chronically draining cyst, immunosuppressive therapy.

Malignant melanoma:

• Malignant tumor of melanocytes.

• Risk: UV, dysplastic nevus syndrome, melanoma history, xeroderma pigmentosum.

• Growth phases: radial (initial), vertical (final).

• Types: superficial spreading melanoma, lentigo maligna melanoma, nodular melanoma, acral lentiginous melanoma.

• Prevention: sunscreen above 15 SPF.

Hair disorders:

Massive hair loss causes:

• Postpartum, oral contraceptive pills, stress, radiation and chemotherapy.

Nail disorders:

• Koilonychias: spoon nails due to iron deficiency.

Additional Reading:

Basic Pathology

1. Cell Injury
2. Inflammation and Repair
3. Immunopathology
4. Water, Electrolyte, Acid-Base, Hemodynamic Disorders
5. Genetic and Developmental Disorders
6. Environmental Pathology
7. Nutritional Disorders
8. Neoplasia
9. Vascular Disorders
10. Heart Disorders
11. Red Blood Cell Disorders
12. White Blood Cell Disorders
13. Lymphoid Tissue Disorders
14. Hemostasis Disorders
15. Blood Banking and Transfusion Disorders
16. Upper and Lower Respiratory Disorders
17. Gastrointestinal Disorders
18. Hepatobiliary and Pancreatic Disorders
19. Kidney Disorders
20. Lower Urinary Tract and Male Reproductive Disorders
21. Female Reproductive and Breast Disorders
22. Endocrine Disorders
23. Musculoskeletal Disorders
24. Skin Disorders
25. Nervous System Disorders
26. Notes on Tissue Regeneration
27. A Table of Bleeding Disorders
28. FAQ on Structure and Function of Red Blood Cells
29. FAQ on Components of Blood
30. Notes on Hemostatic Mechanisms
31. What is Fever?
32. What is Edema?
33. FAQ on Blood Pressure
34. FAQ on principles of fluid and flow dynamics of Blood
35. Causes of Thrombocytopenia
36. Squamous cell carcinoma of head and neck mucosa
37. Four tumors which never metastasize to the brain
38. What is caustic injury?
39. What causes Peripheral Edema?

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