A 3-year-old boy who presented with an acute cerebellar ataxia and x-ray evidence of apparent chest infection, caused by massive infiltration of Langerhans histiocytes, is reported from the Department of Pediatrics, University of Catania, Italy, Northampton General Hospital, and John Radcliffe Hospital, Oxford, UK. Ataxia and slurred speech had been present for 6 weeks before admission. Brain CT and MRI were normal. Chest X-ray showed widespread reticulonodular shadowing, suggestive of mycoplasma pneumonia or metastatic disease. After 2 days treatment with erythromycin for presumed pneumonia, the patient was readmitted as an emergency because of vomiting, drowsiness, and dyspnea, and he died soon after arrival. Autopsy revealed bilateral tension pneumothorax, diffuse bronchiectatic cavities, and generalized congestion of meningeal vessels. Histologically the lungs and spleen were infiltrated by Langerhans cells. The cerebellum showed focal gliosis associated with Purkinje cell loss. 
COMMENT. The diagnosis of Langerhans’ cell histiocytosis (LCH) is made by the electron micrograph finding of Birbeck granules, membranous cytoplasmic structures, 200-400 nm in width and shaped like tennis rackets, and CD1a and S-100 protein antigen on the cell surface . The presentation is usually as bone lesions and dermatitis, hepatosplenomegaly, lymphadenopathy, pancytopenia, fever, and weight loss. CNS manifestations are rarely cerebellar, and usually present with diabetes insipidus from hypothalamic or pituitary infiltration. In the rare cases of cerebellar involvement cited in the pediatric literature, symptoms were chronic and progressive and presented years after LCH diagnosis. The absence of cerebellar infiltration supports a paraneoplastic syndrome and immune mediated mechanism. In the above case report, the primary LCH location was lung involvement. In the N Engl J Med report (Feb 14, 2002), the primary location of LCH was a retro-orbital spenoid sinus mass, and the presenting symptom was frontal pain (see below in Headache section).