Cauda equina lipoma presenting as acute neuropathic arthropathy of the knee. A case report.

A 36-year-old man with a painless, rapidly progressive, destructive lesion of the right knee proved to have neuropathic arthropathy. Rather than being a tumor, the destructive process was neuropathic in origin. Myelography revealed an unsuspected intradural lesion, which proved to be a benign lipoma, at the third and fourth lumbar levels. Excision of the lipoma and arthrodesis of the knee were successful. True intrathecal lipomas are rare lesions that become symptomatic during a period of many years; when they are removed the prognosis is generally good. As in the present case, in neuropathic joint disease the underlying neuropathy and its etiology may be quite subtle, joint destruction may be very rapid, and diagnosis is difficult.