The significance of cerebrospinal fluid analysis in the differential diagnosis of 564 psychiatric patients: Multiple sclerosis is more common than autoimmune-encephalitis.

The analysis of cerebrospinal fluid (CSF) is an essential tool for the differential diagnosis of psychiatric disorders caused by autoimmune inflammation or infections. Clear guidelines for CSF analysis are limited and mainly available for schizophrenia and dementia. Thus, insights into CSF changes in psychiatric patients largely derive from research. We analyzed the clinical and CSF data of 564 psychiatric patients without pre-existing neurological diagnoses from March 1998 to April 2020. Primary aim was to detect previously undiagnosed neurological conditions as underlying cause for the psychiatric disorder. Following CSF analysis, 8 % of patients (47/564) were diagnosed with a neurological disorder. This was the case in 12.0 % (23/193) of patients with affective disorders, 7.2 % (19/262) of patients with schizophrenia, and 4.0 % (23/193) of patients with anxiety disorders. The predominant new diagnoses were multiple sclerosis (19/47) and autoimmune encephalitis (10/47). Abnormal CSF findings without any implications for further treatment were detected in 17.0 % (94/564) of patients. Our data indicates that CSF analysis in patients suffering from psychiatric disorders may uncover underlying organic causes, most commonly multiple sclerosis and autoimmune encephalitis. Our findings imply that the incorporation of CSF analysis in routine psychiatric assessments is potentially beneficial.