Are CASPR2 autoantibodies associated with autoimmune neurologic syndromes?

CASPR2 autoantibodies are strongly associated with a distinctive autoimmune neurologic spectrum that can involve both the central and peripheral nervous systems. This is clinically relevant when cognitive decline, memory symptoms, seizures, and neuromyotonia-like features occur together or evolve over time.

Clinical evidence

• In a major cohort, limbic encephalitis occurred in 42% and Morvan syndrome in 29% of CASPR2-antibody–positive patients. Limbic presentations commonly include cognitive impairment, prominent memory dysfunction, and temporal-lobe seizures.
• Peripheral nerve hyperexcitability—often termed neuromyotonia—produces cramps, stiffness, fasciculations, myokymia, and impaired muscle relaxation. Morvan syndrome may combine these peripheral symptoms with encephalopathy, autonomic disturbance, and severe insomnia.
• The phenotype extends beyond the core manifestations: a systematic review reported cerebellar syndrome in 14.7% (24/163) of cases, and neuropathic pain was a presenting feature in 18% in a major cohort.

Diagnostic interpretation

• A positive CASPR2 result is most meaningful when it matches a compatible clinical syndrome. Isolated, low-titer serum reactivity does not by itself establish autoimmune encephalitis or explain nonspecific cognitive symptoms.
• Serum testing is generally more sensitive, whereas CSF positivity is particularly associated with encephalitic/limbic presentations. Paired serum and CSF testing using a validated CASPR2-specific cell-based assay is therefore important, with confirmation where appropriate.
• Alternative causes of cognitive change, seizures, pain, and peripheral hyperexcitability still require assessment, particularly in an older adult in whom multiple neurologic and systemic conditions may coexist.

Bottom line

• CASPR2 autoantibodies are well-supported markers of autoimmune neurologic syndromes involving cognitive and memory dysfunction, seizures, and peripheral nerve hyperexcitability; their diagnostic value depends on validated testing and close phenotype concordance.