Clinical Course of Adult Idiopathic Syringomyelia: A Retrospective Cohort Study

Idiopathic syringomyelia (IS) in adults is rare, and its clinical course remains poorly defined. This study aimed to describe the clinical and radiological course of adult IS and to assess the relationship between imaging change and clinical outcome.

Retrospective single-center study (2010-2025) including adult patients with IS after exclusion of secondary causes on whole-spine and craniovertebral junction MRI, including flow-sensitive sequences. The absence of a secondary cause was established by a senior neuroradiologist and confirmed on independent review by two neurosurgeons. Maximal anteroposterior syrinx diameter was measured on T2-weighted MRI (sagittal plane to localize the level of maximal diameter, axial plane for the measurement itself), interpreted by the senior neuroradiologist and re-read by the neurosurgeons. Given the physical resolution limits of spinal MRI, a post hoc, clinically meaningful threshold of ≥2 mm was applied as a sensitivity analysis for radiological change. Association between continuous radiological change and clinical outcome was assessed using Pearson and Spearman coefficients with 95% confidence intervals (CI).

Among 357 patients with syringomyelia, 26 (7.3%) were classified as idiopathic. Radiological follow-up was available for 20/26 patients (77%), following exclusion of 6 patients (loss to follow-up, unreliable retrieval of prior imaging, or absence of a comparable repeat MRI; Fig. 1); median follow-up was 23 months (interquartile range [IQR] 8-56; mean 36 months). New or additional symptoms, mostly mild, were reported by 17 patients (65%, 95%CI 46-81%); of these, 7 patients (27%, 95%CI 14-46%) met criteria for clinically significant worsening (new neurological symptoms or aggravation of pre-existing symptoms impacting daily function). Four patients (15%) improved. No patient developed a motor deficit or required surgery during follow-up. Using the ≥2 mm threshold, no patient (0/20) showed a clinically meaningful increase or decrease in syrinx diameter; all 20 evaluable patients were radiologically stable by this criterion. No significant correlation was found between continuous radiological change and clinical outcome (Pearson r=0.18, 95%CI -0.30 to 0.59, p=0.47; Spearman ρ=0.18, 95%CI -0.29 to 0.59, p=0.46), although the study was underpowered to exclude a small-to-moderate association. results CONCLUSIONS: In this retrospective single-center cohort, adult idiopathic syringomyelia was characterized by frequent new or mildly additional symptoms but limited severe neurological deterioration, while clinically meaningful radiological progression, defined using a post hoc, clinically meaningful threshold applied as a sensitivity analysis, was absent in the evaluable cohort. Clinical evolution was far more variable than radiological evolution, and radiological change did not correlate with clinical course, although this cohort had limited statistical power. These findings are hypothesis-generating and do not, by themselves, establish an optimal follow-up strategy for adult idiopathic syringomyelia.