One of the differentials of a subacute neurological deficit (usually with a fluctuating course) is autoimmune neurologic disorders. This can encompass anything from neuropathic symptoms, to cerebellar pathology, to encephalitis-like picture. A personal or family history of autoimmune disease or malignancy should heighten suspicion, and the CSF is likely an inflammatory CSF profile as well (pleocytosis). Neural autoantibodies confirm the diagnosis, and are usually performed in both the serum and the CSF. Most laboratories perform a global screen for a number of potential antibodies that fit the concerning clinical picture, rather than one or two tests.
In addition, autoimmune CNS pathology is concerning for a paraneoplastic syndrome e.g. teratoma, lymphoma or small cell lung cancer.
Take Home Message: If suspecting an autoimmune pathology due to the risk factors and subacute nature of the disease, obtain some extra CSF to run the necessary tests after consulting with neurology.
Tobin WO, Pittock SJ. Autoimmune Neurology of the Central Nervous System. Continuum 2017;23(3):627–653.