Background and aims Neuromyelitis optica spectrum disorder (NMOSD) is a group of uncommon demyelinating disorders characterised mainly by myelitis and opticus neuritis together with highly specific anti-aquaporin-4 antibodies. Case reports of patients with systemic lupus erythematosus (SLE) and NMOSD have been reported. Though myelitis and opticus neuritis are well described, they are rare manifestations of SLE and it is not known to what extent NMOSD contributes to these symptoms. We investigated the occurrence of NMOSD in a large cohort of patients with SLE.

Methods We identified all cases of myelitis and opticus neuritis in a single centre cohort comprising 610 SLE patients, identified during the period 1995–2014. Medical files were reviewed and frozen serum samples from patients with these symptoms were investigated for the presence of anti-aquaporin-4 antibodies.

Results 3 of 5 patients with myelitis and 0 of 1 patient with opticus neuritis were positive for IgG anti-aquaporin-4 antibodies. All patients positive for anti-aquaporin-4 antibodies presented with longitudinal extended transverse myelitis; lesions extending for more than three spinal segments.

Conclusions Among 6 cases with SLE and typical NMOSD symptoms we detected anti-aquaporin-4 antibodies in 3/5 patients with myelitis but not in any of the opticus neuritis cases. NMOSD seems to be a fairly common cause of SLE associated myelitis, accounting for 60% of SLE cases with myelitis in our study. SLE patients with engagement of the spinal cord or optic nerve should be screened for anti-aquaporin-4 antibodies. This is important since rituximab rather than cyclophosphamide is the preferred treatment for NMOSD