Dermatology

Question 1

Describe the structire of the skin generally and in relation to blistering.

Answer 1

Question 2

What are the common causes of skin blistering?

Answer 2

• Inherited - epidermolysis bullosa, bullous ichyosiform erythroderma, bullous cutaneous porphyrias.
• Aquired
  
  • Drug-induced: fixed drug eruption, Stevens-Johnson syndrome toxic epidermal necrolysis
  • Infections: Bullous impetigo, staphylococcal scalded skin syndrome
  • Autoimmune: Linear IgA disease, bullous pemphigoid, pemphigus, dermatitis herpetiformis
  • Other: insect bites, severe sunburn, phytophotodermititis

Question 3

Discuss the differences between pemphigus and bulloous pemphigoid (both autoimmune bullous disorders).

Answer 3

Question 4

Describe what causes dermatitis herpetiformis, how it present and is diagnosed and treat?

Answer 4

• Clinical presentation
  
  • grouped papules/vesicles/urticarial wheals on an erythematous base, associated with intense pruritus, burning, stinging, excoriations
  • lesions grouped, bilaterally symmetrical
  • common sites: extensor surfaces of elbows/knees, sacrum, buttocks, scalp
• Pathophysiology
  
  • transglutaminase IgA deposits in the skin alone or in immune complexes leading to eosinophil and neutrophil infiltration
  • 90% have HLA B8, DR3, DQWZ
  • 90-100% associated with an often subclinical gluten-sensitive enteropathy (i.e. celiac disease)
  • 30% have thyroid disease; increased risk of intestinal lymphoma in untreated comorbid celiac disease; iron/folate deficiency is common
• Investigations
  
  • biopsy
  • immunofluorescence shows IgA deposits in perilesional skin
• Treatment
  
  • dapsone for pruritus (sulfapyridine if contraindicated or poorly tolerated)
  • gluten-free diet for life

Question 5

Describe what causes porphyria cutanea tarda, how it presents and its diagnosis and treatment.

Answer 5

• Clincial presentation
  
  • tense vesicles/bullae in photoexposed areas subjected to trauma
  • facial hypertrichosis, vesicles, and bullae in photodistribution (dorsum of hands and feet), milia, scarring
  • common sites: light-exposed areas subjected to trauma, dorsum of hands and feet, nose, and upper trunk
• Pathophysiology
  
  • autosomal dominant or sporadic skin disorder associated with the presence of excess heme precursors
  • associated with hemochromatosis, alcohol abuse, DM, drugs (estrogen therapy, NSAIDs), HIV, hepatitis C, increased iron indices
• Investigations
  
  • urine + 5% HCl shows orange-red fluorescence under Wood’s lamp (UV rays)
  • 24 h urine for uroporphyrins (elevated)
  • stool contains elevated coproporphyrins
  • immunofluorescence shows IgE at dermal-epidermal junctions
• Treatment
  
  • discontinue aggravating substances (alcohol, estrogen therapy)
  • phlebotomy to decrease body iron load
  • low dose hydroxychloroquine

Question 6

Describe the neurophysiology of itch.

Answer 6

• Itch, like pain, can originate anywhere along the neural itch pathway, from the central nervous system (brain and spinal cord) to the peripheral nervous system and the skin.
• Mechanisms underlying pruritus are complex.
  • The itch signal is transmitted mainly through small, itch-selective C-fibres in the skin in addition to histamine-triggered and non-histaminergic neurons.
  • These connect with secondary neurons which cross the opposite side of the spinothalamic tract and ascend to parts of the brain involved in sensation, emotion, reward and memory. These areas overlap with those activated by pain.
  • Patients with chronic pruritus usually have both peripheral and central hypersensitisation (heightened reaction) which means they tend to overreact to noxious stimuli which normally inhibit itch (such as heat and scratching) and also misinterpret non-noxious stimuli as an itch (eg, light touch).

Question 7

Summarise the main types of itch

Answer 7

• Localised
  
  • Typical causes
    
    • Scalp: seborrhoeid dermatitis, head lice
    • back: grover disease
    • Hand: contact dermatitis
    • legs: venous eczema
    • feet: rinea pedis
  • Neuropathic causes
    
    • face: trigeminal trophic syndrome
    • arm: brachoradial pruritus
    • Dermatomal: herpes zoster
• Systemic
  
  • Metabolic: uraemia, hepatogenic
  • Haematological: polycythaemia vera and iron deficiency anaemia
  • Endocrine: thyrotoxicosis, DM
  • Paraneoplastic: Hodgkin lymphoma, leukaemia, solid organ tumours
  • Infections: HIV, hep C

Question 8

How is itch diagnosed?

Answer 8

• detailed history
• complete physical, including rectal and pelvic examination
• blood work: CBC, ESR, Cr/BUN, LFT, TSH, fasting blood sugar, stool culture and serology for parasites, if on palms with no rash check bile acids, especially in pregnancy

Question 9

How is itch treated?

Answer 9

• treat underlying cause
• cool water compresses to relieve pruritus
• bath oil and emollient ointment (especially if xerosis is present)
• topical corticosteroid and antipruritics (e.g. menthol, camphor, phenol, mirtazapine, capsaicin)
• systemic antihistamines: H1 blockers are most effective, most useful for urticaria
• phototherapy with UVB or PUVA
• doxepin, amitryptyline
• gabapentin, pregabalin
• naloxone
• immunosuppressive agents if severe: steroids and steroid sparing

Question 10

72 yo lady presents with fever and this painful rash.

What is the diagnosis, Rx and complications of this disease?

Answer 10

• Erysipelas: is a strept pyogenes infections of hte deep and subcutis
• Rx: IV ABx - benzylpenicillin and erythromycin
• Complications include sepsis, cerebral abscess and venous sinus thrombosis.