Nephropathic cystinosis: fibrosing colonopathy can also be seen long after introduction of delayed release cysteamine.

Cystinosis is a rare autosomal recessive lysosomal storage disorder characterized by systemic cystine accumulation. Cysteamine is the only currently approved cystine-depleting therapy, available in immediate- and delayed-release (DR cysteamine) formulations. DR cysteamine contains methacrylic acid copolymer, an excipient associated with fibrosing colonopathy in patients with cystic fibrosis. Here, we report on a case of a 10-year-old girl with cystinosis who developed severe gastrointestinal symptoms following long-term treatment with DR cysteamine. Imaging and endoscopy revealed colonic stenosis, and required hemicolectomy. Histopathology showed fibrosing colonopathy characteristics with deposition of birefringent foreign material in the lumen. This case suggests a possible association between prolonged exposure to DR cysteamine and fibrosing colonopathy, highlighting the need for further investigation. Considering the potential severity of this complication, increased clinical vigilance is warranted, especially in the context of the increasing use of this formulation.