The U.S. Food and Drug Administration approved a drug that treats a rare autoimmune disease of the central nervous system. The disease affects the optic nerves and spinal cord.

The drug approved is Enspryng (satralizumab-mwge). The disease it treats is neuromyelitis optica spectrum disorder (NMOSD) in adults with a particular antibody — patients who are anti-aquaporin-4 or AQP4 antibody-positive, according to the FDA.

"Until last year, there were no FDA-approved treatments for patients with this rare, debilitating and sometimes fatal disease. Now there are three," said Billy Dunn, M.D., director of the Office of Neuroscience in the FDA's Center for Drug Evaluation and Research, in an FDA press release.

"In patients with NMOSD, the body's immune system mistakenly attacks healthy cells and proteins in the body, most often those in the optic nerves and spinal cord. Individuals with NMOSD typically have attacks of optic neuritis, which causes eye pain and vision loss. Approximately 50% of patients with NMOSD have permanent visual impairment and paralysis caused by NMOSD attacks. Estimates vary, but NMOSD is thought to impact approximately 4,000 to 8,000 Americans."

Enspryng was tested in two, 96-week clinical studies. The first study included 95 adult patients and the second study had 76 adult patients.

Enspryng is prescribed with a warning for increased risk of infection, including serious and potentially fatal infections, according to the FDA. Those infections include potential reactivation of hepatitis B and tuberculosis.

According to the FDA: "Other warnings and precautions for Enspryng include elevated liver enzymes, decreased neutrophil counts and hypersensitivity reactions. The most common side effects observed were the common cold (nasopharyngitis), headache, upper respiratory tract infection, inflammation of the lining of the stomach, rash, joint pain, extremity pain, fatigue and nausea. Vaccination with live-attenuated or live vaccines is not recommended during treatment and should be administered at least four weeks before starting Enspryng."