Retroperitoneal unicentric Castleman disease presenting with paraneoplastic pemphigus

Castleman disease is a benign lymph node hyperplasia with two histological subtypes. In the case reported here, a young adult male presented with mucocutaneous lesions mimicking common dermatological conditions. Suspicion of an underlying systemic disease arose when the routine clinical care of the skin lesions failed to cure them. Immunoprecipitation and histological analysis of the lesions pointed towards paraneoplastic pemphigus. The radiological imaging of the abdomen showed a retroperitoneal tumour which supported the paraneoplastic nature of the skin disease. Preoperative biopsy of the retroperitoneal tumour could not provide a definitive diagnosis. So, complete surgical excision of the retroperitoneal tumour was undertaken and pathological evaluation led to the final diagnosis of Castleman disease. We explain how the varied atypical presentation of an underlying rare disease can lead to a delay in the diagnosis, and how we untangled it with sequential work-up leading to successful surgical excision of the disease.