Researchers say that diagnosis and management of encephalopathies may need to be rethought, as many patients who test negative for the relevant antibody still benefit from immunotherapy.
Of 48 patients with a diagnosis of probable autoimmune encephalopathy, only 21 (44%) individuals were positive for antibodies known to be associated with this type of encephalopathy. However, both antibody-positive and antibody-negative patients responded to immunotherapy, with complete recovery achieved in 20 (42%) children, after a mean follow-up period of 24 months.
In an analysis of 111 samples from pediatric encephalopathy patients, 48 children with at least one of the features neuropsychiatric symptoms, seizures, movement disorder, or cognitive dysfunction were diagnosed as having encephalopathy that was probably immune-mediated.
Testing of these children's samples showed that 21 were antibody positive, with 13 (27%) having antibodies to N-methyl-D-aspartate receptor, seven (15%) antibodies to voltage-gated potassium channel-complex proteins, and one (2%) antibodies to glycine receptor.
The team reports that, overall, there were no differences in clinical features between the positive and negative groups. The most common presenting features were seizures (83%), behavioral changes (63%), and confusion (50%). Twenty-seven patients (56%) had neuropsychiatric symptoms and 18 (56%) developed a movement disorder. In addition, 25 (52%) required intensive care for seizure control or reduction in consciousness level.
As reported in the Journal of Neurology, Neurosurgery & Psychiatry, 34 (73%) of the patients were treated with immunotherapy. First-line immunotherapies (corticosteroids, intravenous immunoglobulins, and plasma exchange) were given to 29 patients, while five required regular immunosuppressive treatment with azathioprine, cyclophosphamide, rituximab, or mycophenolate.
Of the treated patients, 32 (94%) showed some response to immunotherapy - 16 in each group. In all, 23 (68%) had a "probable" response, while nine (28%) had a "definite" response, and there were no differences in treatment responses between the antibody-positive and antibody-negative groups.
Of 14 patients who did not receive any immunotherapy, only four (29%) completely recovered from their condition at a mean follow-up period of 24 months, compared with 16 (47%) of 34 who received therapy. The antibody-positive group had slightly worse outcomes, with only six (29%) compared with 14 (27%) in the antibody-negative group making a complete recovery. Nevertheless, the authors note, disability as judged by modified Rankin scores showed a trend toward improvement between nadir and final follow up in both groups.
"Thus it appears that the lack of identification of a known antibody by current available methods should not exclude the diagnosis autoimmune encephalopathy, and immunotherapy could be considered.
"The similarities between patients with and without identified antibodies indicate a need to search for new antigenic targets that could be helpful in future diagnosis," they add.
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