A 16-month-old boy presented with cervical lymphadenopathy and a mediastinal mass causing tracheal displacement. Treatment of what at first was suspected to be a malignant neoplasm was limited to low-dose irradiation of the mediastinum and biopsy excision of the cervical lymph nodes. There has been no recurrence of disease in the subsequent four years.
The pathological features and clinical course correspond to a benign disease first described in 1969 in which there is massive proliferation of histiocytes in lymph node sinuses. No infectious cause was identified. Consistent but eventually reversible defects in lymphocyte response to phytohaemagglutinin and in augmentation of nitro-blue tetrazolium reduction by neutrophils during phagocytosis were demonstrated in the patient and in his monozygous twin. These defects in cellular immune function are believed to be important in the pathogenesis of the histiocytosis.