Malabsorption and Small Bowel Disease — Written Clinical Reasoning

Part A — Diagnosis

The diagnosis is coeliac disease, established by the combination of:

1. Compatible clinical features (weight loss, chronic diarrhoea, and iron deficiency anaemia).
2. Positive serology — anti-tTG IgA at 14 times the upper limit of normal and anti-endomysial IgA positive, with a normal total IgA (1.2 grams per litre), excluding selective IgA deficiency.
3. Diagnostic duodenal histology — Marsh 3c total villous atrophy with crypt hyperplasia and increased intraepithelial lymphocytes (45 per 100 enterocytes, above the threshold of 30). ^[1]

The microcytic iron deficiency anaemia (MCV 71, ferritin 4) is the expected consequence of proximal small bowel disease: iron is absorbed predominantly in the duodenum, the site most affected by coeliac enteropathy. Iron deficiency anaemia is in fact the single most common adult presentation of coeliac disease ^[1]. The pruritic vesicular rash on extensor surfaces is dermatitis herpetiformis, the cutaneous manifestation of coeliac disease, which would show granular IgA deposition at the dermoepidermal junction on skin biopsy ^[1].