The clinical features and outcome of scan-negative and scan-positive cases in suspected cauda equina syndrome: a retrospective study of 276 patients.

Background: The majority of patients presenting with suspected clinical cauda equina syndrome (CES) have no identifiable structural cause for their symptoms ('scan-negative' CES). Understanding these patients aids clinical differentiation and management in CES.

Methods: A retrospective electronic note review was undertaken of patients presenting with suspected CES, defined as ≥ 1 of acute bladder, bowel, sexual dysfunction or saddle numbness, to a regional neurosciences centre. We investigated radiology, clinical features, psychiatric and functional disorder comorbidities and outcome of patients with 'scan-negative' CES and patients with MRI confirmed compression of the cauda equina ('scan-positive' CES).

Results: 276 patients were seen over 16 months. There were three main radiologically defined patient groups: (1) 'scan-positive' CES (n = 78, mean age 48 years, 56% female), (2) 'scan-negative' CES without central canal stenosis but with lumbosacral nerve root compression not explaining the clinical presentation (n = 87, mean age 43 years, 68% female) and (3) 'scan-negative' CES without neural compromise (n = 104, mean age 42 years, 70% female). In the two 'scan-negative' groups (no neural compromise and nerve root compression), there were higher rates of functional disorders (37% and 29% vs. 9%), functional neurological disorders (12% and 11% vs 0%) and psychiatric comorbidity (53% and 40% vs 20%). On follow-up (mean 13-16 months), only 1 of the 191 patients with 'scan-negative' CES was diagnosed with an explanatory neurological disorder (transverse myelitis).

Conclusions: The data support a model in which scan-negative cauda equina syndrome arises as an end pathway of acute pain, sometimes with partly structural findings and vulnerability to functional disorders.