Theorell J, Ramberger M, Harrison R, et al. - In first-episode psychosis (FEP) patients admitted to psychiatric care, formes frustes of autoimmune encephalitis were not prevalent. Screening for neuronal surface autoantibodies in unselected psychotic patients is not supported.

• According to a hypothesis, a subgroup of patients with FEP suffer from a forme fruste of autoimmune encephalitis.

• A prospectively ascertained clinically well-characterized cohort of 71 FEP patients without traditional neurological features, as well as 48 healthy controls, were included.

• Testing of serum and cerebrospinal fluid (CSF) for autoantibodies against seven neuronal surface autoantigens was performed employing live cell-based assays.

• These revealed 4% (3/71) patient sera with weak binding to either contactin-associated protein-like 2, the NMDAR (N-methyl-d-aspartate receptor) or glycine receptor vs no binding from 48 control samples (p = 0.28, Fisher’s test).

• No CSF autoantibodies were detected in the three seropositive persons and they exhibited no differences from the autoantibody-negative patients in their clinical phenotypes, or across multiple parameters of peripheral and central inflammation.

• For CSF NMDAR antibodies, all individuals were negative.