Pictorial Case Study: Blistering rash

The Case - This 32-year-old woman attended the surgery complaining of a recurrent, very itchy, papular, blistering rash. It had appeared over her knees, elbows, buttocks and scalp.

Dermatitis herpetiformis: autoimmune disease (Photograph: Author image)
Dermatitis herpetiformis: autoimmune disease (Photograph: Author image)

She had applied calamine lotion and tried an oral antihistamine, without benefit. On examination there were obvious papules, vesicles and blisters and excoriated lesions over the buttocks and upper thighs and signs of scars from scratch marks in other areas. There were no digestive symptoms, such as indigestion, bloating, change in bowel habit or weight loss.

Diagnosis and Management
A possible diagnosis of dermatitis herpetiformis (DH) was made. DH is a genetically linked, autoimmune disease associated with a gluten sensitive enteropathy. The rash develops as the result of the deposition of IgA in the papillary dermis, caused by an immunological response to chronic stimulation of the mucosa of the gut by gluten.

However, many patients with this condition have no GI symptoms. About 15-25 per cent of patients with coeliac disease develop DH. DH is more common in northern Europe, it usually presents in the 20 to 40 year age group and is more common in men.

The diagnosis is confirmed by direct immunofluorescence of a skin biopsy. Serum markers, such as IgA endomysial antibodies, may be positive.

The main approach to treatment is to advise the patient on a gluten-free diet. The diet must be adopted for life but it may take several months for improvement to occur. Dapsone is usually added initially and should achieve dramatic improvement. Itching in this patient settled within 24 hours.

Patients on long-term treatment with dapsone are at risk of developing blood disorders and acute haemolytic anaemia or agranulocytosis that would make them susceptible to infections. This is a particular risk for patients with glucose-6-phosphate dehydrogenase deficiency. This level should be checked before starting the medication and the patient warned to report any such problems promptly.

POSSIBLE DIFFERENTIAL DIAGNOSES

  • Bullous pemphigoid.
  • Erythema multiforme.
  • Dermatitis artefacta.
  • Scabies.
  • Eczema.
  • Papular urticaria.

 

DIFFERENTIAL DIAGNOSIS
Bullous pemphigoid

  • Thought to be caused by IgG immunoglobulins and activated T-lymphocytes that attack proteins causing an autoimmune reaction to the proteins.
  • Tends to occur in middle age and the elderly.
  • Itchy and tense blisters especially in the flexures. May affect the mouth.
  • Diagnosis confirmed by biopsy of a typical blister and by direct immunofluorescence.
  • Systemic steroids (prednisolone) starting with 40-80mg daily.
  • Very potent topical steroids may be sufficient for mild or localised cases and may be tried first or as an adjunct to systemic therapy. Tetracycline or nicotinamide may also be tried.
  • Other drugs that may be used in resistant cases are azathioprine, methotrexate, cyclophosphamide and ciclosporin.
  • Severe cases may require hospital admission.
  • Remission usually occurs within five years.

Contributed by Dr Jean Watkins, a retired GP in Hampshire.

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