Early Treatment Improves Outcomes in Neuromyelitis Optica Spectrum Disorder

HILTON HEAD, SC—Neuromyelitis optica spectrum disorder (NMOSD) can result in severe disability, but early diagnosis and treatment increase the likelihood that a patient will regain his or her baseline function, according to an overview provided at the 41st Annual Contemporary Clinical Neurology Symposium. Increased understanding of NMOSD has led to new diagnostic criteria, and emerging data are clarifying the question of effective treatments.

NMOSD As a Distinct Disorder

NMOSD originally was recognized as an inflammatory disorder of the CNS that causes transverse myelitis and optic neuritis, said Siddharama Pawate, MD, Associate Professor of Neurology at Vanderbilt University Medical Center in Nashville. Although neurologists first considered NMOSD a variant of multiple sclerosis (MS), the former has several features that distinguish it from the latter. These features include exceptionally severe relapses, spinal cord lesions that span more than three vertebral segments, and CSF that reveals pleocytosis and high protein levels. In addition, some MS treatments such as interferons, fingolimod, and natalizumab usually exacerbate, rather than mitigate, NMOSD.

Siddharama Pawate, MD

In 2004, researchers found that antibodies against aquaporin-4 (AQP4) were almost 100% specific for NMOSD. Astrocytes and ependymal cells, but not oligodendrocytes or neurons, express AQP4. When anti-AQP4 antibodies bind to the membrane of an astrocyte, they disrupt the blood–brain barrier and eventually cause the astrocyte to die. The death of astrocytes promotes secondary damage of oligodendrocytes and neurons. Because of these processes, swelling in the spinal cord and the optic nerve are prominent features of NMOSD on MRI, said Dr. Pawate. The swelling, in turn, can lead to vascular compromise and necrosis, thus accounting for the severity of myelitis in NMOSD.

Clinical Presentations of NMOSD

Approximately 75% of patients with NMOSD present with optic neuritis. The next most common clinical presentation is transverse myelitis, which may include paraparesis or quadriparesis, loss of sensation, and bladder or bowel dysfunction. About 35% of patients present with transverse myelitis. Optic neuritis and transverse myelitis occur simultaneously in about 10% of patients who present with NMOSD. “Unlike the MS lesions that are mostly in the white matter, NMOSD lesions in the spinal cord involve gray matter and white matter,” said Dr. Pawate. Other clinical features specific to NMOSD include severe neuropathic pain, tonic spasms that last for as long as 90 seconds, and pruritus. The latter symptom responds well to gabapentin, said Dr. Pawate.

NMOSD entails more severe optic neuritis than that associated with MS. It can be bilateral and lead to complete loss of vision. Optic neuritis usually is longitudinally extensive in NMOSD. A lesion length of 17.6 mm suffices to distinguish NMOSD from MS, and a length of more than 35 mm is approximately 100% specific for the former disorder. Swelling can cause necrosis in the optic nerve and result in poor recovery of vision. Furthermore, homonymous hemianopsia can happen in NMOSD due to damage to the optic tracts, but is rare in MS.

The clinical presentation of NMOSD also may include area postrema syndrome, which entails intractable nausea and vomiting. Patients may have cerebral or cerebellar lesions, symptomatic narcolepsy, or endocrine dysfunction (eg, syndrome of inappropriate antidiuretic hormone secretion).