To describe patients with isolated contactin-associated protein-1/contactin-1 complex-IgG (Caspr1/CNTN1-complex-IgG) and those with Caspr1-IgG, either alone or combined with Caspr1/CNTN1-complex-IgG.

Among 15 identified patients; nine had detailed clinical information. Five patients (60% males) were Caspr1/CNTN1-complex-IgG positive, while four (50% males) were CASPR1-IgG positive.  The median age at symptom onset was 47 years (range 35-56) among Caspr1-IgG patients, and 35 years (range 6-54) in those with Caspr1/CNTN1-complex-IgG. An acute to subacute onset, often mimicking Guillain-Barre syndrome, was observed in three (60%) Caspr1/CNTN1-complex-IgG patients and one (25%) Caspr1-IgG patient. Distal predominant weakness occurred in all Caspr1-IgG and 80% of Caspr1/CNTN1-complex-IgG patients. Sensory ataxia was present in all Caspr1/CNTN1-complex-IgG patients and half of the Caspr1-IgG patients. Prominent neuropathic pain was reported in all Caspr1-IgG patients but was less frequent in the Caspr1/CNTN1-complex-IgG group (60%). None of the patients exhibited renal involvement or paraproteinemia. Enlarged nerve roots were noted in one Caspr1-IgG and one Caspr1/CNTN1-complex-IgG patients. Refractoriness to IVIG was a common feature, seen in all Caspr1-IgG patients and in the majority (75%) of Caspr1/CNTN1-complex-IgG patients who received it. Rituximab was effective in all treated patients (three Caspr1-IgG and one Caspr1/CNTN1-complex-IgG).

Patients with isolated Caspr1/CNTN1-complex-IgG commonly present with acute onset/rapid progression, and sensory ataxia. In contrast, Caspr1-IgG seropositive cases more frequently had prominent neuropathic pain. Despite these distinct characteristics, both groups commonly exhibit refractoriness to IVIG and respond well to rituximab, similar to other more common autoimmune nodopathies.