Short Follow-up Bias Confounds Estimates of the "Typical" Clinical Course of Susac Syndrome.

BACKGROUND

To evaluate the validity of the prevailing concept that Susac syndrome (SS), a rare microvasculopathy of the brain, retina, and inner ear, is a self-limiting disease.

METHODS

We performed a literature search to identify all cases of SS reported between 1973 and October 2015. If available, we determined their demographics, duration of follow-up, and the clinical course that was labeled as monocyclic or polycyclic. We attempted to determine the number of relapses and the relapse rate in patients with polycyclic disease.

RESULTS

Our literature search yielded 185 relevant publications reporting 405 cases of SS. The duration of follow-up could be determined in 247/405 cases, with a range 0.5-312 months. The mean was 41 months but the distribution was skewed, with a median of 24 months. Defining the clinical course as monocyclic or polycyclic was possible in 102 patients who were followed for greater than 24 months; 53 were identified as having a polycyclic course. Patients labeled polycyclic were followed longer than those labeled monocyclic (median 62 vs 42 months, P < 0.001). The number or frequency of attacks per patient could not be determined.

CONCLUSIONS

The follow-up of published cases of SS is short, creating an inherent bias toward the impression that the disease is self-limiting. Our findings suggest that stratification of SS into monocyclic, polycyclic, and chronic continuous courses may oversimplify the phenotype of SS; instead, the possibility of a relapsing-remitting course must be considered in all patients with this disorder.