Markedly elevated cerebrospinal fluid white blood cell count in multiple sclerosis: How high is too high?

The diagnosis of multiple sclerosis (MS) is based on the revised McDonald's criteria, which includes clinical history, neurological examination, MRI findings and cerebrospinal fluid (CSF) analysis necessitating the exclusion of alternative explainable diagnoses. Markedly elevated CSF white blood cells (WBCs) over 50 (units) is considered a "red flag" for an alternative diagnosis apart from MS.

To present a man with typical relapsing-remitting MS (RRMS) despite markedly elevated CSF WBCs.

A 33-year-old man presented with progressive bilateral numbness and weakness following a mild respiratory infection. Initial brain MRI showed cerebral white matter lesions and a left lateral pontine T2 hyperintense lesion. Cervical spine MRI showed demyelinating lesions at C3, C5 and C6 levels. CSF analysis revealed elevated white blood cell counts of 1,347 with lymphocytic predominance of 79 %, elevated unique oligoclonal bands, and immunoglobulin (Ig)G index. Comprehensive tests excluded other diagnoses, including infectious such as meningitis and encephalitis, autoimmune disorders such as neuromyelitis optica (NMO) and myelin oligodendrocyte glycoprotein-associated disease (MOGAD), and nutritional deficiencies.

Follow-up cervical spine MRI at 22 months revealed a new demyelinating C2 lesion, and he initiated ocrelizumab. Over four years of follow-up, he had no new clinical attacks or radiological activity and maintained a normal neurological examination.

Markedly elevated CSF WBC counts may occur in otherwise typical RRMS and are not always a red flag to an alternative diagnosis.