• Clinical science

Collection of dermatological disorders


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

Sebaceous and epidermoid cysts

  • Definition
  • 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


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
  • 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



  • 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
Miliaria crystallina Miliaria rubra Miliaria profunda
  • Most common type
  • Rare; usually seen in adult men in tropical climates, who have had repeated episodes of miliaria rubra
Clinical findings


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


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!


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
  • Management
    • Protection from light and avoidance of sun exposure
    • Frequent skin cancer screening, retinoids as prophylaxis
  • Prognosis: severely limited life expectancy


Pseudofolliculitis barbae

  • Definition: inflammatory skin disorder caused by shaving
  • Epidemiology: most common in black men (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: firm, hyperpigmented, tender, pruritic papules and pustules on beard area
  • Diagnosis: clinical appearance
  • Treatment
    • Cessation of shaving; alternative hair-removal techniques (e.g., laser hair removal)
    • Adjunctive: topical treatments (e.g., retinoids, corticosteroids, antimicrobials)



  • 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
  • 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