Atypical Cauda Equina Syndrome with Lower Limb Clonus: A Literature Review and Case Report

Cauda equina syndrome (CES) is a neurosurgical emergency warranting urgent surgical decompression. Treatment delay may precipitate permanent adverse neurological sequelae. CES is a clinical diagnosis, corroborated by radiological findings. Atypical presentations should be acknowledged to avoid inappropriately rejected diagnoses. We report the case of a woman exhibiting bilateral lower limb weakness, perineal numbness, sphincter disturbance, and lower limb clonus. Classically, CES displays lower motor neuron signs in the lower limbs. The presence of clonus, an upper motor neuron sign, brought the diagnosis into doubt. The history included chronic fatigue, difficulty mobilizing, and intermittent blurred vision. A lumbosacral magnetic resonance imaging (MRI) scan demonstrated a large disc prolapse at L5/S1. The cord was not low-lying or tethered. Therefore, the possibility of second diagnoses, including of inflammatory or demyelinating nature, was raised. An urgent MRI scan of the brain and cervicothoracic cord identified no other lesions. On balance, the clinical presentation could overwhelmingly be attributed to the L5/S1 disc prolapse. Given the time-critical nature of cauda equina (CE) compression, an urgent laminectomy and discectomy was offered with continued postoperative investigation of the clonus. Intraoperatively, significant CE compression was found. The operation proceeded uneventfully and the patient recovered fully. In the immediate postoperative period, the clonus persisted yet subsequently resolved completely. We conclude that the clonus was attributable to CE compression and not a second pathology. The corresponding neuroanatomical correlate remains nondelineated. The presence of clonus does not preclude a diagnosis of CES. If the clinicoradiological information otherwise correlate, surgery should not be delayed while alternative diagnoses are sought. The literature is also reviewed.