• Clinical science

Collection of dermatological disorders

Sebaceous and epidermoid cysts


Cat scratch disease

  • Definition: benign, self-limiting infectious disease that is transmitted mainly by cats (scratching, biting, or licking)
  • Pathogen: Bartonella henselae (gram-negative bacillus, aerobic)
  • Epidemiology: predominantly affects young adults and children
  • Clinical features
  • Diagnosis
    • Bacterial culture from blood, swabs, or lymph node aspirate
    • Antibody testing
    • Histological study:
      • Warthin-Starry staining; of involved lymph node may demonstrate clusters of bacilli.
      • H&E staining of cutaneous lesions may demonstrate granulomas.
  • Treatment
    • Usually not needed
    • Azithromycin is indicated for severe, persistent, or debilitating disease


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 the trunk, neck, and intertriginous areas
  • Therapy
Miliaria crystallina Miliaria rubra Miliaria profunda
  • Most common type
  • Rare; usually seen in adult males in tropical climates
Level of sweat duct blockage
  • Deep blockage at the dermo-epidermal junction
Clinical findings
  • Firm, erythematous papule of 1–4 mm
  • Characteristically reduced sweating from the blocked duct


Nummular eczema (nummular dermatitis)

  • Definition: chronic, inflammatory skin condition; that is 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
    • Affects primarily the extremities
  • Therapy


Gianotti-Crosti syndrome

  • Definition: maculopapular exanthem; association with viral infections, especially hepatitis B and Epstein-Barr Virus (EBV)
  • Epidemiology: peak incidence in children up to 6 years of age
  • Clinical findings
    • Affects the face, buttocks, and extensor surfaces of the extremities affected
    • Possibly pruritus
    • Self-limiting, ranging between 10 days and 6 months duration
  • Treatment: symptomatic


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

Dyshidrotic eczema

Erythema ab igne

  • Translation: “redness from fire”
  • Definition: reticular erythema with teleangiectasias
  • Etiology: chronic heat application (infrared radiation, hot water bottles)
  • Course: with continued heat exposure → marbled, brownish hyperpigmentation caused by increased melanin production


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

Pitted keratolysis (keratoma plantare sulcatum)

  • Definition: pit-like corneal defects on the soles of the feet with a severe burning sensation
  • Epidemiology: particularly affects the feet of the individuals working in a hot, humid environment (for e.g., athletes, laborers, and soldiers posted in tropical climates)
  • Etiology: caused by maceration and various bacteria; most often occurs when footwear is not sufficiently breathable

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 women aged 20–30 years of age, and children
  • Etiology: unknown; presumably caused by regular application of (glucocorticoid) creams and 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
    • Avoidance of cosmetics, drugs containing corticoids
    • If necessary, local or systemic tetracycline

SAPHO syndrome

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

Livedo reticularis

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

Benign livedo

  • Pathophysiology: autonomic dysregulation; (functional disturbance) causing slowed cutaneous perfusion in response to external factors (e.g., cold)
  • Epidemiology: higher incidence in young women
  • Clinical findings
    • Symmetrical; livedo reticularis (regular, small, round) on the extremities and sometimes trunk
    • Triggered by the cold and regresses after application of warmth
  • Treatment: warmth, alternately cold and warm baths, sauna
  • 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 → minimal UV radiation can lead to severe skin damage, and has carcinogenic effects
  • Clinical findings
  • Management:
    • Complete protection from light and avoidance of sun exposure
    • Frequent skin cancer screening, retinoids as prophylaxis
  • Prognosis: severely limited life expectancy


Pseudofolliculitis barbae

  • Epidemiology: most common in black males (hair shafts with a tendency to 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 hair-growing areas (beard)
  • Diagnosis: clinical appearance; culture is usually negative
  • 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 are noticed early in life (e.g., newborns, toddlers)
  • Classification
  • Pathophysiology: impaired melanin production
    • Due to dysfunctional tyrosinase activity, or impaired transport of tyrosine or melanin.
    • Normal melanocyte number, 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
    • Sunscreen, avoidance of sunburns, regular screening for skin cancer
    • Dark, tinted glasses
    • Nitisinone : used for hereditary tyrosinemia type 1