CPC04 Extranodal Rosai–Dorfman disease: a multisystem presentation with rectal involvement and transient amaurosis

Abstract Rosai–Dorfman disease (RDD), or sinus histiocytosis with massive lymphadenopathy, is a rare non-Langerhans cell histiocytic disorder. While classical RDD presents as painless cervical lymphadenopathy, extranodal involvement occurs in approximately 40% of cases. Cutaneous RDD is common, but gastrointestinal involvement, particularly the rectum, is extremely rare, occurring in 1% of patients. We report the case of a 67-year-old man presenting with headache and a highly unusual episode of total blindness lasting 3 days followed by gradually improving peripheral vision loss. He was noted to have a widespread asymptomatic papular rash, which was biopsied twice, both consistent with cutaneous RDD. There was a total absence of palpable lymphadenopathy. Systemic imaging with computed tomography (CT), positron emission tomography–CT and magnetic resonance imaging demonstrated mild mesorectal lymphadenopathy and a large (4 cm increasing to 7 cm) rectal mass in the absence of gastrointestinal symptoms. This contradicts the classic ‘massive lymphadenopathy’ presentation of the disease. Histopathological examination of biopsied rectal tissue confirmed histiocytosis consistent with RDD. This case highlights the diagnostic challenge of ‘pure’ extranodal RDD. The transient blindness suggests potential central nervous system and orbital involvements, which are also documented but rare manifestations of the disease. The presence of a large rectal mass further emphasizes the need to consider RDD in the differential diagnosis of atypical gastrointestinal tumours. Dermatologists must maintain a high index of suspicion for systemic RDD when evaluating biopsy-proven skin lesions, even in the absence of lymphadenopathy. A multidisciplinary approach involving gastroenterology, neurology and radiology is essential for managing the diverse extranodal manifestations of this variable disease.