Distinguishing CNS neurosarcoidosis from multiple sclerosis and an approach to "overlap" cases

Neurosarcoidosis is an important diagnosis to exclude in the work-up for suspected multiple sclerosis (MS). The distinction between the two conditions is usually possible due to characteristic clinical manifestations, magnetic resonance imaging (MRI) findings, and the results of other supportive investigations such as CT-PET. Definitive diagnosis can be made by histopathological examination, but this is not always practical. Misdiagnosis can occur when the clinical characteristics and MRI findings of both conditions overlap. Those patients with characteristic findings of MS but extraneural histopathological evidence of sarcoidosis are a particularly difficult diagnostic group. Diagnostic clarity is essential to inform treatment, especially as certain treatments for one disorder can exacerbate the other. This article summarises the clinical, laboratory and radiological findings that aid the clinician in distinguishing between the two conditions. It also discusses the literature on the potential for sarcoidosis and MS to co-exist in some patients, and how to approach the treatment of these "overlap" patients.