Explaining a cutaneous sign of systemic disease — OSCE

Candidate instructions (8-minute station)

You are the paediatric registrar in the clinic. A 10-year-old girl has an intensely itchy, symmetric eruption of grouped vesicles and crusts over the elbows, knees and buttocks, present for four months, with poor sleep from the itch. The family asks what the rash is, whether it is just an allergy, and why the doctor wants blood tests and a gut biopsy for a skin problem. [6]

Your tasks are: [6]

1. Explain the diagnosis of dermatitis herpetiformis in plain, reassuring language, including that it is not a simple allergy but the skin sign of an immune reaction to gluten. [6]
2. Explain why coeliac blood tests and a small-bowel biopsy are needed for a skin problem, and what they are looking for. [5]
3. Explain the treatment — a strict gluten-free diet and dapsone for rapid itch control — and the safety checks for dapsone. [5]
4. Set the expectation for the long term, including why treating the gut matters even when the gut is silent. [5]

You are not expected to perform the biopsy or start dapsone without the specialist — those decisions are made with the gastroenterologist and dermatologist. [6]

Examiner prompt to the actor (parent)

"It is just a rash, isn't it? She has always been a bit itchy, and I thought it was an allergy to the washing powder. Why does she need blood tests and a camera down her throat for a skin problem — that sounds like a lot for a rash? And if it is this coeliac thing, is it serious? Will she grow properly?" [6]

Marking domains

• Frame and explanation (3): explains that the rash is dermatitis herpetiformis, the skin sign of coeliac disease, an immune reaction to gluten rather than a simple allergy, in plain reassuring language; names that the skin and the gut share the same gluten-driven immune process. [6]
• Investigation rationale (3): explains why coeliac serology and a duodenal biopsy are needed for a skin problem — because the blood test finds the gluten antibodies and the biopsy shows whether the small bowel is affected, and almost every child with this rash has gut involvement even when silent. [5]
• Treatment and safety (2): explains the strict gluten-free diet as the definitive treatment that clears the skin over months, and dapsone for rapid itch control while the diet takes effect, with the glucose-6-phosphate dehydrogenase screen and blood monitoring. [5]
• Long-term plan (2): explains why treating the gut matters — growth, iron levels, bone health and the small long-term lymphoma risk — even when the gut is silent, and sets up the gastroenterology and dietitian referral and the coeliac surveillance. [5]

Model answer — the explanatory script

"Thank you for bringing her in. I can see how itchy this is and how much it is disturbing her sleep, and I want to explain what we think is going on and why we need to look beyond the skin." [6]

"Let me answer your questions one at a time — what the rash is, why we need the tests, the treatment, and the long term." [5]

"First, what it is. The rash is called dermatitis herpetiformis, and the important thing is that it is not a simple allergy like a reaction to washing powder. It is the skin sign of coeliac disease, which is an immune reaction to gluten — a protein in wheat, barley and rye. In coeliac disease, the immune system reacts to gluten in the gut, and in some children that same immune reaction also shows up in the skin as these intensely itchy blisters. So the skin and the gut share the same underlying problem, and that is why we need to look at both." [6]

"Second, why the blood tests and the biopsy. The blood tests look for the gluten antibodies — if they are there, they tell us the immune system is reacting to gluten. The small-bowel biopsy, done with a camera while she is asleep, takes a tiny sample of the lining of the gut to see whether it is inflamed by the gluten. We do the biopsy because almost every child with this skin rash has some gut inflammation, even when she has no tummy symptoms at all — the gut can be silent while the skin is not. So the tests are not over-treating a rash; they are finding the disease the rash is pointing to. We keep her on gluten until the biopsy is done, because stopping gluten first can make the tests normal and hide the diagnosis." [5]

"Third, the treatment. The definitive treatment is a strict, lifelong gluten-free diet, and the good news is that the skin clears on the diet over a few months as the gut heals. For the itch, while we are waiting for the diet to work, we use a medicine called dapsone that switches the skin inflammation off quickly. Before we start dapsone we do a blood test for an enzyme called G6PD, because in some people dapsone can affect the blood, and we monitor her blood while she is on it. Once the diet is working, we taper the dapsone off, so the long-term treatment is the diet, not the medicine. We will work with a gastroenterologist and a dietitian to get this right." [5]

"Fourth, the long term, and your question about whether it is serious. The good news is that coeliac disease is very manageable with the diet, and children grow and thrive on it. The reason we take it seriously is that if the gut inflammation is left untreated, over the years it can affect her growth, her iron levels and her bone strength, and there is a small increase in a long-term risk that we reduce by sticking to the diet. So even though her tummy feels fine now, treating the gut with the gluten-free diet protects her growth and her health for the future, not just her skin. The skin that clears on the diet is the gut that has healed." [5]