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A 67-year-old man reported progressive numbness and weakness in both legs. The numbness had started in the right buttock 4 weeks before, progressing down the posterio-medial leg to the lateral foot, and evolving into a painful, burning sensation. He developed similar symptoms in the left leg 1 week later, with urinary hesitancy. Over the following 3 weeks, he started dragging the right foot and walking unsteadily. He had no back pain, preceding trauma, viral illness, systemic or craniobulbar symptoms, and no weakness or sensory symptoms in his arms or trunk. He had hypertension and diabetes and took irbesartan and metformin.
On examination, his mental status, cranial nerves and upper limbs were normal. Lower limb tone was normal with no atrophy, spasticity or clonus. There was asymmetric distal weakness in right ankle dorsiflexion (2/5), inversion (4/5), eversion (3/5) and left ankle dorsiflexion (4+/5). Lower limb reflexes were absent other than the right patellar reflex and plantar responses were flexor. Sensory examination showed only distal symmetrical reduced vibration sensation to the shins. Perianal sensation and rectal tone were normal. Postvoid residual volume was 50 mL. There were no root tension signs. Gait was normal based, unsteady. Romberg sign was negative.
Question 1: what is the likely localisation and differential diagnosis?
He has progressive, asymmetric lower limb weakness and areflexia with diffuse neuropathic pain, but no upper motor neuron signs or sensory level. This suggests a peripheral nervous system process with bilateral involvement of the lumbosacral plexus, nerve roots or multiple nerves. The most important immediate differential is acute cauda equina syndrome, given the asymmetry, pain and urinary symptoms; this can be due to structural, infective or inflammatory polyradiculopathies. A conus medullaris lesion is less likely, as this is typically gives a symmetric presentation and hyper-reflexia. Non-traumatic plexopathies such as diabetic amyotrophy is a further alternative. Stepwise progression and pain may suggest a …
Contributors LM-O: drafting/revision of the manuscript for content, including medical writing for content; major rolein the acquisition of data. JC: drafting/revision of the manuscript for content, including medical writing for content; major role inthe acquisition of data. SM: drafting/revision of the manuscript for content, including medical writing for content. TC: drafting/revision of the manuscript for content, including medical writing for content; major role inthe acquisition of data; study concept or design; analysis or interpretation of data; supervision.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed by Simon Rinaldi, Oxford, UK.