Abstract
Pellagra is a multisystem disorder caused by niacin (vitamin B3) deficiency, which typically presents with dermatitis, diarrhoea, and dementia. Although it has become less prevalent in developed countries due to improved nutrition and the fortification of foods with niacin, isolated cases continue to emerge among vulnerable groups. We present a case of a 50-year-old woman with a complex psychiatric and neurological history who developed a widespread, scaly, erythematous rash unresponsive to corticosteroids, along with progressive dysphagia, diarrhoea, and neurocognitive decline. Initial investigations and management focused on suspected dermatomyositis. However, the clinical picture evolved despite steroid treatment and extensive investigations. Following the discovery that she followed a restrictive ketogenic diet over several years, a clinical diagnosis of pellagra was made, and treatment with nicotinamide and B-vitamin supplementation led to rapid and sustained resolution of all her symptoms. This case underscores the importance of considering pellagra in patients presenting with neuropsychiatric and dermatologic symptoms, even in modern healthcare settings. Early recognition is essential as untreated pellagra can be fatal, despite the fact that treatment with nutritional therapy is straightforward.