Infections in the differential diagnosis of Bell's palsy: a plea for performing CSF analysis

Peripheral facial nerve palsy (FP) is the most common single nerve affection. Most cases are idiopathic, but a relevant fraction is caused by potentially treatable aetiologies including infections. Not all current diagnosis and treatment guidelines recommend routine cerebrospinal fluid (CSF) analysis in the diagnostic workup of this symptom. In this study, we evaluated frequency of aetiologies and relevance of CSF analysis in an interdisciplinary cohort. We retrospectively analysed all cases of newly diagnosed FP treated at a German university medical centre in a 3-year period. Diagnostic certainty was classified for infectious aetiologies according to clinical and CSF parameters. 380 patients with FP were identified, 63 children and 317 adults. Idiopathic BellA ' s palsy was predominant in 61 %. 25 % of FP was attributed to infections, and other causes were identified in 14 %. Clinical presentation alone was not conclusive for infectious aetiology, in almost half of patients with infection-attributed FP the reported symptoms or clinical signs did not differ from common symptoms of idiopathic Bell`s palsy. Determination of C-reactive protein or white blood cell count was not helpful in the identification of infectious causes, and radiological imaging was performed in a high proportion of adult patients without conclusive results. Nuchal rigidity was found only in 7 % of patients with CSF pleocytosis. The predominant infectious agents were Borrelia burgdorferi, VZV and HSV, and in most of these cases diagnosis relied on the findings of CSF analysis. This study outlines the importance of careful differential diagnosis to identify infectious causes of facial nerve palsy. The high incidence and frequent unspecific clinical presentation of infectious FP underlines the importance of including CSF analysis in the diagnostic routine workup of FP.