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AS Cauda Equina — SCE Rheumatology MCQ

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HardSpondyloarthropathyAS Cauda EquinaSCE Rheumatology

A 62-year-old man with ankylosing spondylitis diagnosed 32 years ago develops 18 months of progressive saddle sensory loss, bilateral lower motor neurone leg weakness and urinary dysfunction, culminating in urinary retention. He is afebrile and his CRP is normal. MRI of the lumbosacral spine shows marked enlargement of the thecal sac, multiple posterior dural diverticula, clumping and adherence of the cauda equina roots, and smooth scalloping of the posterior vertebral bodies and neural arches. There is no disc extrusion or extradural collection. Which pathological process most likely underlies this rare neurological complication?

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Correct answer: E — Chronic adhesive arachnoiditis with lumbosacral dural ectasia

Explanation lettering: B = shown as A · C = shown as B · D = shown as C · E = shown as D · A = shown as E

A is correct. Ankylosing spondylitis-associated cauda equina syndrome is a rare late complication that usually evolves insidiously with sensory, motor and sphincter dysfunction. Characteristic imaging shows lumbosacral dural ectasia, arachnoid diverticula, cauda equina root clumping or tethering, and smooth pressure erosion of adjacent bone. Chronic adhesive arachnoiditis and dural fibrosis are proposed to impair cerebrospinal fluid dynamics, producing ectasia and progressive root injury. Metastatic disease and epidural infection would usually produce an extradural mass or collection; infection would also be more likely with pain, fever or inflammatory-marker elevation. Conus infarction has an abrupt onset and does not cause dural ectasia. A central disc extrusion would be visible as a focal compressive lesion.

Reference: Tang C et al. Cauda Equina Syndrome in Ankylosing Spondylitis: Challenges in Diagnosis, Management, and Pathogenesis. Journal of Rheumatology. 2019;46:1582-1588. https://pubmed.ncbi.nlm.nih.gov/30936280/