Summary

This learning card covers various dermatological disorders, including sebaceous and epidermoid cysts, cat scratch disease, cutaneous mastocytosis, miliaria, nummular eczema, angiokeratoma, dyshidrotic eczema, livedo reticularis, xeroderma pigmentosum, pseudofolliculitis barbae, and albinism.

Sebaceous and epidermoid cysts

Definition
- Epidermoid cyst
  - Most common cutaneous cyst
  - Lined by stratified squamous epithelium and contains keratin
- Sebaceous cyst: cyst formed by blockage of the sebaceous gland; contains sebum
Clinical findings
- Slow-growing, mobile, firm, painless nodule
- Dark-colored punctum; may be seen on a sebaceous cyst.
- Localized predominantly on the face, head, neck, back, or genitals
- Infection; possible (causes painful, erythematous mass that may exude pus)
- High probability of recurrence
Treatment
- Asymptomatic cysts do not need treatment
- Intralesional steroids (triamcinolone) may help reduce inflammation
- In case of infection or pressure symptoms; : total surgical excision
- Oral antibiotics for infected cysts

References:^[1]^[2]^[3]^[4]

Cat scratch disease

Definition: benign, self-limiting infectious disease that is transmitted mainly by cats (via scratching, biting, or licking)
Pathogen: Bartonella henselae (gram-negative bacillus, aerobic)
Epidemiology: predominantly affects children and adolescents
Clinical features
- General: malaise, loss of appetite, fever
- Localized
  - One or more 5–10 mm large, erythematous, non-tender cutaneous papules or vesicles develop approx. 4–6 days after exposure (in > 50% of cases) at the site of inoculation.
  - Swollen, tender lymph nodes 1–3 weeks following exposure
    - Develops as primary lesions disappear
    - Usually unilateral, occasionally suppurative
    - Most commonly involves lymph nodes of axillae, neck, or groin (nearest the site of inoculation)
    - Resolves after 2–4 months
- In immunocompromised individuals
  - Bacillary angiomatosis
  - Hepatic peliosis
  - Bacteremia and endocarditis
Diagnosis
- Bacterial culture from blood, swabs, or lymph node aspirate
- Antibody testing
- Histological study
  - Warthin-Starry staining of the involved lymph node may show clusters of rod-shaped bacteria.
  - H&E staining of cutaneous lesions may show necrotizing granuloma formation.
Treatment
- Mild or moderate cases: azithromycin (5-day course) to decrease lymphadenopathy and the duration of illness
- Persistent and/or disseminated cases (e.g., bacillary angiomatosis): erythromycin (or doxycycline); in case of CNS involvement or endocarditis, rifampicin should be used in combination with one of these drugs.

References:^[5]^[6]^[7]^[8]^[9]

Cutaneous mastocytosis (urticaria pigmentosa)

Definition: a condition characterized by proliferation and accumulation of mast cells in the skin
Epidemiology: mainly affects children
Clinical features
- Maculopapular cutaneous mastocytosis (MPCM)
  - Reddish-brown papules, macules, plaques, or nodules on the extremities, trunk, face and scalp
  - Pruritis and skin flushing is common after exposure to triggers
- Darier sign: localized erythema and urticaria following mechanical irritation (e.g., rubbing, scratching) of the skin or skin lesions that are rich in mast cells
- Acute systemic anaphylactic reactions : abdominal pain, diarrhea, and syncope
Diagnosis
- Usually a clinical diagnosis
- Laboratory studies (CBC, liver function tests, tryptase levels) to rule out systematic mastocytosis
- Skin biopsy for definitive diagnosis
Treatment: supportive treatment only; no curative treatment available
- Avoid triggers of mast cell degranulation
- Antihistamines, mast-cell stabilizer (cromolyn)
- Refractory cases: topical glucocorticoids, PUVA therapy
Prognosis: 80% of cases in children resolve spontaneously before the onset of puberty

References:^[10]

Miliaria

Definition: transient, papular exanthem following exposure to heat
Etiology: blockage of the eccrine sweat ducts in hot and/or humid environments
Localization: : mainly on the trunk, neck, and intertriginous areas
Therapy
- General measures to reduce sweating: wearing light, breathable fabrics, removing occlusive bandages, etc.
- Topical steroids; (hydrocortisone, triamcinolone), topical antibiotics for pustular eruptions (clindamycin, erythromycin)

Types
	Miliaria crystallina	Miliaria rubra	Miliaria profunda
Epidemiology	Very common in neonates	Most common type	Rare; usually seen in adult men in tropical climates, who have had repeated episodes of miliaria rubra
Clinical findings	Clear 1–2 mm vesicles with no erythema	Erythematous 2–4 mm papules, may become inflamed and pus-filled (miliaria pustulosa) Itching or stinging pain, exacerbated by sweating	Firm, erythematous papule of 1–4 mm Reduced sweating from the blocked duct

References:^[11]

Nummular eczema (nummular dermatitis)

Definition: chronic inflammatory skin condition; characterized by well-demarcated round lesions
Etiology: : multifactorial; primarily an immunological hypersensitivity reaction; (dermatitis) due to xerosis and damage to the epidermal lipid barrier
Clinical findings
- 2–5 cm large, coin-shaped, well-demarcated erythematous plaques
- Pruritus, scabs
- Primarily affects the extremities
Therapy
- Symptomatic
  - Skin hydration with wet wraps and lotions
  - Oral antihistamines
- Topical steroids and immune modulators; (tacrolimus and pimecrolimus) to decrease inflammation

References:^[12]^[13]

Angiokeratoma

Definition: benign ectasia of the superficial dermal blood vessels with characteristic hyperkeratosis of the papillary dermis
Clinical features
- Asymptomatic papules, plaques, or verrucous skin lesions
  - Red, blue, or black in color
  - Usually solitary; less commonly diffuse
  - Most commonly located on the lower extremities and groin
- Associated with Fabry disease: multiple skin lesions located on the trunk
Diagnosis
- Usually a clinical diagnosis
- Skin biopsy: telangiectasia, acanthosis, hyperkeratosis
Treatment: laser ablation, mainly a cosmetic procedure

References:^[14]

Dyshidrotic eczema

Definition: a condition characterized by a recurrent, acute blistering eczema of the palms and/or soles
Etiology
- Unknown; believed to be multifactorial.
- Risk factors include:
  - Atopic dermatitis
  - Irritant contact dermatitis
  - Allergic contact dermatitis (e.g., nickel, cobalt, balsam of Peru, perfumes)
  - Dermatophyte infections
Clinical features
- Acute, recurrent episodes of pruritic vesicular/bullous eruptions on the palms, lateral aspects of the fingers, and/or soles
  - Warm weather exacerbates symptoms.
  - The lesions are usually multiple and deep-seated.
- Severe cases include dystrophic nail changes (e.g., color changes, ridge formation)
Diagnosis ^[14]
- Usually a clinical diagnosis.
- Skin biopsy
  - To rule out differential diagnoses (e.g., psoriasis) or in case of poor response to treatment.
  - Findings include intraepidermal spongiotic vesicles/bullae without involvement of the eccrine sweat glands.
Treatment ^[14]
- Avoid triggers (e.g., allergens and irritants such as metals, perfumes, or cigarette smoking)
- Appropriate skincare (i.e., wash hands with lukewarm water and soap-free cleanser; apply emollients after drying hands adequately)
- Topical corticosteroids for mild cases that do not respond to general measures; oral corticosteroids for severe cases.
- Consider adding PUVA or UVA treatment for patients with refractory disease.
Complications
- Chronic hand dermatitis: lichenification, scaling, fissured patches and plaques
- Secondary infection (e.g., Staphylococcus aureus)

Livedo reticularis

Definition: a vascular syndrome that can be caused by either benign autonomic dysregulation of cutaneous perfusion or pathological obstruction of blood vessels

Physiological livedo

Pathophysiology: autonomic dysregulation; (functional disturbance) causing slowed cutaneous perfusion in response to external factors (i.e., cold)
Epidemiology: incidence highest in young women
Clinical findings
- Symmetrical; livedo reticularis (regular, small, round) on the extremities and sometimes the trunk
- Triggered by cold, regresses after application of warmth
Treatment: warmth, sauna, alternating cold and warm baths
Prognosis: improves with age

Pathological livedo

Pathophysiology: localized obstructions slow the blood flow (organic disturbance)
Etiology: vascular diseases (cholesterol embolism, atherosclerosis, vasculitis)
Clinical findings
- Irregular; , unusual livedo reticularis of the extremities and sometimes trunk
- Persists after warming the skin
Treatment: treat the underlying disease

Livedo reticularis that does not regress after application of warmth is indicative of an underlying vascular disease and requires treatment!

References:^[15]

Xeroderma pigmentosum

Definition: rare, autosomal-recessive, hereditary skin disease caused by defective DNA repair mechanisms (i.e., nucleotide excision repair); in affected individuals, minimal UV radiation can lead to severe skin damage and has carcinogenic effects
Clinical findings
- Extreme sensitivity to light with pigmentary changes
- Development of multiple precancerous lesions; (actinic keratoses) and eventually malignant skin cancer; (basal cell carcinoma, spinocellular carcinoma, melanoma) already in early childhood
Management
- Protection from light and avoidance of sun exposure
- Frequent skin cancer screening, retinoids as prophylaxis
Prognosis: severely limited life expectancy

References:^[16]

Pseudofolliculitis barbae

Definition: inflammatory skin reaction in response to short hair that becomes entrapped within the skin
Etiology
- Usually occurs due to shaving (also known as razor bumps)
- Most common in African American men because the hair shafts typically form tight coils
Pathophysiology
- Extrafollicular penetration: Hair enters the interfollicular epidermis after it exits the follicular orifice.
- Transfollicular penetration: Hair penetrates the dermis before exiting the follicular orifice.
Clinical findings
- Lesions: firm, hyperpigmented, tender, pruritic papules and pustules
- Location: beard region (i.e., cheeks, jaw, and neck)
Diagnosis: clinical appearance
Treatment
- Cessation of shaving; alternative hair-removal techniques (e.g., laser hair removal)
- Adjunctive: topical treatments (e.g., retinoids, corticosteroids, antimicrobials)

References:^[17]

Albinism

Definition: : congenital disorders of melanin synthesis resulting in hypopigmentation
Epidemiology
- Affects all races and both sexes
- Most types of albinism are congenital and noticed early in life (e.g., newborns).
Classification
- Ocular albinism (OA): Only the visual system (e.g., iris, retina) is affected.
- Oculocutaneous albinism (OCA): absence of melanin in the skin, hair, and the visual system
  - May be associated with Chédiak-Higashi syndrome
Pathophysiology: impaired melanin production
- Due to dysfunctional tyrosinase activity, or impaired transport of tyrosine or melanin
- Normal melanocyte levels, decreased or absent melanin production
Clinical features
- Eyes
  - Translucent, hypopigmented blue, grey, or green irides
  - Photophobia, decreased visual acuity
  - Strabismus, nystagmus, amblyopia
  - Abnormalities of the optic nerve
- Skin and hair: milky white color, photosensitivity, sunburns
- Associated with increased risk of skin cancer
Treatment: only supportive treatment, no curative treatment available
- Treatment of strabismus: eye-patching , eye surgery
- Avoidance of direct exposure to UV light and regular screening for skin cancer
- Wearing (prescription) sunglasses
- Nitisinone : used for the treatment of hereditary tyrosinemia type 1

References:^[18]

Waardenburg syndrome

Definition: a congenital pigmentation disorder due to abnormal migration of melanocytes during embryogenesis
Etiology: autosomal dominant inherited disorder
Clinical features
- Patchy depigmentation of the hair and skin (e.g., poliosis)
- Pale blue eyes or heterochromia iridum
- Broad nasal root
- Congenital hearing loss
- Cleft lip and palate
- Neural tube defects
- Associated with Hirschsprung disease
Treatment: only supportive treatment, no curative treatment available

References:^[19]