• Clinical science

Collection of dermatological disorders


This article 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


Cat scratch disease


Cutaneous mastocytosis (urticaria pigmentosa)



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: 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
  • Treatment: laser ablation, mainly a cosmetic procedure


Dyshidrotic eczema

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 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
  • Diagnosis: clinical appearance
  • Treatment
    • Cessation of shaving; alternative hair-removal techniques (e.g., laser hair removal)
    • Adjunctive: topical treatments (e.g., retinoids, corticosteroids, antimicrobials)




Waardenburg syndrome