Encephalopathy with upper body hypertonia and myoclonus in patient with systemic lupus erythematosus and anti-CASPR2

Systemic lupus erythematosus (SLE) may involve the nervous system but there are no specific biomarkers of neuroSLE. Limbic encephalitis has been rarely associated with SLE. We present a case of a 22-year-old black woman where typical SLE psychosis evolved to an encephalopathy with atypical features, normal MRI, electroencephalogram slowing and frontal and occipito-temporal hypometabolism on fluorodeoxyglucose positron emission tomography (FDG PET).Memory deficits, bizarre behaviour, psychosis, neuromyotonia and movement disorders have been described in autoimmune central nervous system disorders and associated with specific antibodies. Brain MRI may be normal and cortical brain hypometabolism on FDG PET scans has been reported. We have not found any report of limbic encephalitis or other SLE neurological manifestation associated to positive titres of anti-CASPR2 antibodies and this may warrant systematic investigation. In the rare cases of limbic encephalitis associated with SLE no specific antibodies were documented. Anti-CASPR2 antibodies have been associated not only with limbic encephalitis but also with neuromyotonia and Morvan syndrome. Although our patient had a specific pattern of tone abnormalities with an impressive cervical and upper limb hypertonicity and flaccid lower limbs, no myotonic discharges were found. We did not find any association between myoclonus and anti-CASPR2 antibodies. We cannot exclude that a non determined autoantibody could have played a role; however, clinical and FDG PET improvement supports an antibody-mediated injury, in this case of neuroSLE.