The patient, who had a longstanding history of ankylosing spondylitis, presented with gait disturbances, sensory impairment at the perineum and bladder dysfunction. An MRI examination of the lumbar spine was performed.
The patient, who had a longstanding history of ankylosing spondylitis, presented with gait disturbances, sensory impairment at the perineum and bladder dysfunction. An MRI examination of the lumbar spine was performed with spin echo T1-weighted and turbo spin echo T2-weighted sequences in the axial and sagittal planes. This revealed an enlargement of the spinal canal with smooth asymmetric erosions of the laminae at multiple levels, enlargement of the dural sac with arachnoid diverticulae and abnormally positioned thickened nerve roots indicative of arachnoiditis (Figs 1,2). Findings consistent with the underlying longstanding ankylosing spondylitis were also evident on sagittal scans.
The cauda equina syndrome is a late and relatively infrequently recognised complication of ankylosing spondylitis (1-4). Pain in the low back, buttocks or legs may be the initial symptoms. The onset is rather insidious and the symptoms may be misinterpreted as evidence of recurrent spondylitis or sacroiliitis. Urinary sphincter disturbances are frequent and may mimic bladder neck obstruction due to prostatic enlargement. Motor impairment is less frequent and associated pain is an inconstant feature (1,3,4). The progression of cauda equina syndrome is most often slow. The pathogenesis of the syndrome remains unknown. Postirradiation ischaemia, demyelination, spinal arachnoiditis and arteriitis with vascular involvement of the nerve roots and radicular degeneration are among the mechanisms proposed (1,5). Spinal arachnoiditis as a complication of ankylosing spondylitis with damage to the nerve roots has been observed in several cases (1,3,5). The arachnoid diverticulae associated with this syndrome probably reflect the result of an inflammatory response affecting the meninges. Arachnoiditis, with formation of adhesions and blind pouches, may progressively expand by means of arterial pulsatile forces transmitted through the cerebrospinal fluid (1).
Radiological investigation may include radiography, myelography, CT or MRI. Asymmetric pedicular, laminar or spinal process erosions confined to one level or involving multiple levels may be shown on radiographs, but are clearly depicted on CT. Erosion of the posterior portion of the vertebral body is an infrequent finding. Myelography and MRI may reveal enlargement of the dural sac with arachnoid diverticulae and findings of arachnoiditis. Owing to the extensive vertebral fusions present in patients with longstanding ankylosing spondylitis, performance of myelography is technically difficult. MRI has a clear advantage over myelography in most cases. The coexistence of typical bone erosions and findings consistent with arachnoiditis, as shown in this case, in a patient with longstanding ankylosing spondylitis is pathognomonic of cauda equina syndrome. Neither medical nor surgical treatment seems to be beneficial (4). Early diagnosis may have a positive effect on the outcome by allowing treatment at an earlier stage of the disease.
Cauda equina syndrome secondary to longstanding ankylosing spondylitis
Based on the provided lumbar MRI images and the patient’s history of ankylosing spondylitis, the following main features are observed:
Based on the patient’s long-term history of ankylosing spondylitis and the radiological findings of vertebral ankylosis/fusion and an enlarged dural sac, the following potential diagnoses should be considered:
Taking into account the patient’s symptoms (gait disturbance, perineal sensory abnormalities, urinary retention or difficulty, and other bladder dysfunction) along with the imaging findings (dural sac enlargement, arachnoid diverticula and adhesions, signs of nerve root involvement), the most likely diagnosis is:
This is a known but relatively rare late complication of ankylosing spondylitis, commonly presenting radiologically with vertebral ankylosis/fusion and the formation of extradural or subarachnoid diverticula.
Currently, there is no widely recognized specific treatment for ankylosing spondylitis complicated by cauda equina syndrome. Overall, it can be approached from the following perspectives:
Given the characteristics of ankylosing spondylitis with cauda equina syndrome, rehabilitation should address both spinal mobility and lower limb strength while protecting nerve function. The following approaches can be considered:
This report is based on the patient’s medical history, imaging data, and current medical literature, and is intended as a reference for analysis. It is not a substitute for an in-person visit or professional medical advice. If the patient has further questions or any change in condition, they should seek prompt medical evaluation.
Cauda equina syndrome secondary to longstanding ankylosing spondylitis
