Erdheim-Chester disease: atypical presentation of a rare disease.

We report the clinical case of an adult patient referred to our hospital because of trismus due to a tumour in the right infratemporal and pterygomaxillary fossa. He referred hyporexia, weight loss and right trigeminal neuralgia. On physical examination, he had trismus and diplopia. On neuroimaging, the tumour invaded the central nervous system affecting the right temporal lobe and orbit, and the sellar region. Tumour biopsy revealed foamy histiocytes and isolated giant multinuclear cells immunoreactive to CD68 and negative to CD1a and S100. A diagnosis of Erdheim-Chester disease was made. Non-evidence of large bone involvement was found in neither plain radiographs nor Technetium 99 m bone scintigraphy. BRAFV600E mutation analysis was negative. Because of raised intracranial pressure, a debulking surgery of the intracranial histiocytic process was performed. The patient improved his symptoms and remains clinically stable after 12 months of treatment with pegylated interferon-α-2a 180 µg/weekly.