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Malignant psoas syndrome: recognition of an oncologic entity.

From January 1985 to January 1989 four patients with advanced cancer developed a syndrome characterized by proximal lumbosacral plexopathy and painful flexion of the ipsilateral hip with positive psoas muscle stretch test. Malignant involvement of the psoas major muscle was confirmed radiologically in all cases. Pain was intractable in 3 patients until time of death. We have termed this presentation the malignant psoas syndrome (MPS) and retrospective review of 427 oncology patients with "high risk" solid cancer culled no additional cases during the same 4-year period. We believe MPS to be a hitherto unreported complication of systemic cancer in which malignant involvement of the psoas muscle, in addition to producing severe nociceptive pain, contributes to the process of lumbosacral deafferentation. The clinical presentation, diagnosis and strategies of management of MPS are discussed.