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Classical Homocystinuria (HCU) is a rare inherited disorder of metabolism caused by deficiency in cystathionine-β-synthase (CBS), leading to accumulation of homocysteine and its precursor methionine. Untreated, there is a risk of thromboembolism as well as complications involving eye, skeleton and brain. We present a case, presenting with complications of chronic pancreatitis, subsequently diagnosed with HCU.A 14-year-old male had a 9 month history of episodic abdominal pain, diarrhoea, vomiting and weight loss. Initial investigations revealed normal Coeliac serology and faecal calprotectin and a raised serum amylase 162 U/L. He developed shortness of breath and a CT scan confirmed a large right sided pleural effusion requiring chest drain insertion. Pleural amylase was raised; 2817 u/L and a pancreatic-pleural fistula secondary to acute on chronic pancreatitis was diagnosed. CT reported pancreatic inflammation, thickened small bowel loops; ischaemic wedge infarct of the liver; portal vein thrombosis and multiple small stones in the gall bladder. He was managed conservatively with total parenteral nutrition (TPN).Labs revealed raised alanine transferase (ALT) 76 U/l (10 – 50 U/l), hypoalbuminaemia 15 g/L (35 – 50 g/L), low fat soluble vitamin levels A, D, E and a coagulopathy; prothrombin time 21 s (normal range 10.0 – 13.2) triggering metabolic investigations. Blood amino acid profile identified elevated plasma methionine (>2000 umol/L) and total homocysteine (tHcy)(>200 umol/L). Classical HCU was diagnosed. Urgent action to reduce TPN protein, reducing the risk of cerebral oedema and thromboembolism, using methionine free PN, proved challenging. IV pyridoxine, folate and anticoagulation were started. Small bowel oedema persisted and Creon (faecal elastase < 15 ug/g stool (> 200 ug/g stool) was started. Nasogastric feeds led to an increase in gastrointestinal symptoms and raised serum lipase. However, nasojejunal feeding enabled transition from TPN to enteral feeding. Plasma methionine (17 umol/l) and tHcy normalised (3.4 umol/L) over 7 weeks. He was discharged home on full nasojejunal feeds and recently has re-establsihed oral eating.Chronic pancreatitis is a rare complication of HCU, possibly caused by thromboembolic events in the vasculature of the pancreas. Only a few cases have been reported in the literature.