Comorbidity between Multiple Sclerosis and Idiopathic Intracranial Hypertension: A Retrospective Cohort Study

Background: Comorbidity between multiple sclerosis (MS) and idiopathic intracranial hypertension (IIH) has been reported in case series as early as the 1990s. Many patients with both MS and IIH will experience both headache and vision loss, which may present a challenging diagnostic quandary. Furthermore, some have hypothesized that shared neuroinflammatory mechanisms may link the two conditions. However, no study to date has systematically evaluated comorbidity between MS and IIH.

Objectives: To systematically evaluate clinical characteristics of patients diagnosed with both MS and IIH.

Methods: We performed a retrospective cohort study of patients seen in the Duke University Health System from Jan 1, 1995 to November 11, 2021. Patients with international classification of diseases (ICD) codes related to MS or IIH or with direct mention of MS or IIH in electronic medical records (including related terms such as pseudotumor cerebri) were manually reviewed, and patients who met both current McDonald criteria for MS and Modified Dandy Criteria for IIH were included.

Results: Thirteen patients met both the McDonald criteria and Modified Dandy Criteria. All patients were female. Eight patients (62%) self-identified as Black, non-Hispanic, and five patients (38%) self-identified as White, non-Hispanic. Eight patients (62%) were initially diagnosed with IIH and later additionally diagnosed with MS; two patients (15%) were initially diagnosed with MS and later additionally diagnosed with IIH; and three patients (23%) were simultaneously diagnosed with both MS and IIH. Median age at MS and IIH diagnosis was 31 and 28 respectively. For patients initially diagnosed with IIH, median time to subsequent MS diagnosis was five years (range 0-15). The two patients initially diagnosed with MS were diagnosed with IIH five and 24 years later. Median body mass index (BMI) at MS and IIH diagnosis were both 39 kg/m². Eight patients had four or more oligoclonal bands on CSF evaluation at time of MS diagnosis, one patient had no oligoclonal bands present, and four patients either did not receive a lumbar puncture or did not have available data on oligoclonal banding. Two patients had at least one episode of optic neuritis after MS diagnosis.

Conclusions: We found that comorbidity between MS and IIH is rare but clearly exists in some patients. Clinicians should be aware of the potential for co-diagnosis as each condition requires a different management strategy.