We present a case of Erdheim-Chester disease (ECD) with diplopia.

A 56-year-old woman came to the hospital with a 6-week history of diplopia on left lateral gaze. The right eye showed mildly limited adduction. Humphrey automated perimetry demonstrated inferior bitemporal quadrantanopia. Orbital and brain magnetic resonance imaging revealed well-defined orbital masses in both intraconal orbits with homogenous enhancement, as well as multiple masses of homogenous signal intensity in the brain. Systemic evaluation showed involvement of the long bones, and retroperitoneum, but no involvement of the heart, or lungs. Incisional biopsy of the right orbital mass was performed. Histopathological examination showed numerous lipid-laden histiocytes and few multinucleated Touton giant cells. Immunohistochemical staining showed positivity for CD68, but negativity for CD1a, and ECD was therefore diagnosed. The patient received treatment with radiation therapy and interferon-α, but died due to sepsis secondary to urinary tract infection after 2 months.

Except exophthalmos, diplopia may be the only initial symptom of an orbital mass. Although rare, the possibility of ECD should be considered in the differential diagnosis of both retrobulbar and orbital masses with diplopia.