Coeliac Disease

Coeliac disease is an immune-mediated enteropathy caused by sensitivity to gliadin, a component of gluten found in wheat, barley, and rye. It affects approximately 1% of the UK population, though many remain undiagnosed. HLA-DQ2 and HLA-DQ8 are the key genetic predispositions. The inflammation primarily occurs in the proximal small intestine (duodenum and jejunum), leading to villous atrophy, crypt hyperplasia, and increased intraepithelial lymphocytes. This reduction in surface area results in malabsorption. Presentation is diverse: classic cases involve chronic diarrhoea, steatorrhoea (oily/foul-smelling stools), and weight loss. However, many present subtly with unexplained iron-deficiency anaemia, lethargy, or dermatitis herpetiformis (an itchy, blistering skin rash). It is frequently associated with other autoimmune conditions like Type 1 Diabetes and Autoimmune Thyroid disease. Diagnosis must be made while the patient is consuming gluten; a minimum of one meal containing gluten daily for 6 weeks is recommended before testing. Initial screening is by IgA tissue transglutaminase (anti-tTG) antibodies. Gold-standard confirmation is a D2 duodenal biopsy. Treatment requires a strict, lifelong gluten-free diet, which leads to mucosal healing and symptom resolution. Complications of untreated coeliac disease include osteoporosis, splenic atrophy (functional hyposplenism), and enteropathy-associated T-cell lymphoma (EATL).

The pathophysiology involves the enzyme tissue transglutaminase (tTG), which deamidates gliadin peptides in the lamina propria. These deamidated peptides are then presented by HLA-DQ2 or DQ8 positive antigen-presenting cells to T-cells. This triggers an inflammatory cascade involving both the innate and adaptive immune systems. Cytotoxic T-cells cause direct damage to enterocytes, leading to the characteristic histological changes: 1. Villous atrophy (flattening of the villi), 2. Crypt hyperplasia (deepening of the crypts to compensate for loss), and 3. Intraepithelial lymphocytosis. This process severely impairs the absorption of nutrients, particularly iron, folate, and fat-soluble vitamins (A, D, E, K). Small bowel involvement is characteristically most severe in the duodenum.

Clinical features can be divided into GI and extra-GI. GI: Chronic or intermittent diarrhoea, steatorrhoea, abdominal pain, bloating, and unintentional weight loss. Extra-GI: Fatigue, iron deficiency anaemia (non-responsive to oral iron), vitamin D deficiency (osteomalacia), aphthous ulcers, and dermatitis herpetiformis. In children, it often presents as failure to thrive and irritability. On examination, look for signs of malnutrition, finger clubbing (rare), or a vesicular rash on the elbows/knees. Given the risk of hyposplenism, patients are more susceptible to encapsulated bacteria (Streptococcus pneumoniae). Patients with Coeliac have a slightly higher risk of malignancy, particularly enteropathy-associated T-cell lymphoma (EATL), which should be suspected if symptoms return despite a strict gluten-free diet.

Initial test: IgA Tissue Transglutaminase (anti-tTG) antibodies AND Total IgA levels (to rule out IgA deficiency, which would give a false-negative tTG). Second-line serology: Anti-endomysial (EMA) antibodies. Diagnostic gold standard: OGD and Duodenal Biopsy showing Marsh criteria changes (villous atrophy). Bloods: FBC (anaemia - microcytic or macrocytic), Ferritin, B12, Folate, LFTs (may have mild elevation), Bone profile (low calcium, high ALP in osteomalacia). Genetic testing: HLA typing (has a high negative predictive value).

Lifelong strict gluten-free diet (avoid wheat, barley, rye). Oats are usually safe but may be cross-contaminated. Refer to a specialist dietitian. Supplementation: Iron, Vitamin D, and Calcium if deficient. Vaccination: Annual flu vaccine and a one-off Pneumococcal vaccine (plus 5-yearly boosters) due to functional hyposplenism. Monitoring: Annual review of symptoms, BMI, and anti-tTG levels (to check compliance). DEXA scan to assess for osteoporosis at diagnosis or menopause.