• 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


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


Cutaneous mastocytosis (urticaria pigmentosa)


  • 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
Level of sweat duct blockage
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


Gianotti-Crosti syndrome

  • Definition: maculopapular exanthem associated with viral infections, especially hepatitis B and Epstein-Barr virus (EBV)
  • Epidemiology: peak incidence in children under 7 years of age
  • Clinical findings
    • Affects the face, buttocks, and extensor surfaces of the extremities
    • Pruritus may occur
    • Self-limiting, lasting between 10 days and 6 months
  • Treatment: symptomatic


  • Definition: benign ectasia of the upper dermal vessels with hyperkeratotic involvement of the papillary dermis
    • Angiokeratoma circumscriptum: verrucous, blue-black plaques located primarily on the extremities
  • Treatment: laser ablation, mainly a cosmetic procedure

Dyshidrotic eczema

  • Definition: multiple, severely itchy, tightly packed clusters of blisters on the palms and soles that contain a clear fluid
  • Etiology: unknown, believed to be multifactorial; in rare cases, a manifestation of allergic contact dermatitis or atopic dermatitis
  • Treatment

Erythema ab igne

  • Definition: Erythema ab igne (from Greek “redness from fire”) is reticular erythema with telangiectasias.
  • Etiology: paralysis of the deep vascular plexus of the skin caused due to chronic heat application (e.g., infrared radiation, hot water bottles)
  • Course: continued heat exposure → marbled, brownish hyperpigmentation due to increased melanin production


  • Callus: thick, toughened skin caused by repeated mechanical pressure and friction
  • Clavus: painful, hyperkeratotic lesion with a center core (corn) caused by frictional forces and trauma

Pitted keratolysis (keratoma plantare sulcatum)

  • Definition: superficial bacterial skin infection with pit-like corneal defects on the soles of the feet accompanied by malodor and a burning sensation
  • Epidemiology
    • Occurs worldwide (especially in athletes, industrial workers, and soldiers)
    • Risk factors include:
      • Hot, humid weather
      • Occlusive footwear
      • Hyperhidrosis
  • Etiology: caused by maceration and various bacteria; most often occurs in association with insufficiently breathable footwear

Localized lipodistrophy

  • Definition: localized degeneration of subcutaneous adipose tissue
  • Etiology: following subcutaneous injections, secondary to certain drugs , pressure-induced, or idiopathic

Perioral dermatitis (stewardess disease)

  • Definition: chronic facial dermatitis affecting the perioral region
  • Epidemiology: primarily children and women 20–30 years of age
  • Etiology: unknown; presumably caused by regular application of (glucocorticoid) creams and/or cosmetics
  • Clinical findings
    • Erythema with grouped papules and pustules
    • Dry skin with painful burning and a sensation of tightness
    • No residual scarring after resolution
  • Treatment
    • Avoid using cosmetics or drugs containing corticoids.
    • In severe cases, local or systemic tetracycline

SAPHO syndrome

  • Definition and clinical findings: rheumatological, spondylarthritic disease with simultaneous occurrence of
  • Etiology: unknown
  • Diagnosis
    • Mainly a clinical diagnosis
    • X‑ray imaging , scintigraphy , and MRI
  • Treatment: primarily symptomatic

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