“The following is a sobering reminder that we need to remain vigilant for other opportunistic CNS (central nervous system) infections in MSers on natalizumab. The case report below is of a MSer developing a severe VZV (varicella zoster virus) retinitis with significant visual loss. Presumably the virus escaped elimination in the periphery and made its way to the retina to cause damage. The virus could not be eliminated by the immune system because natalizumab blocked trafficking of lymphocytes into the eye. This type of viral retinitis is usually only seen in patients with AIDS and other diseases associated with severe immunosuppression. What this case illustrates is that natalizumab reduces trafficking of immune cells into the posterior compartment of the eye. PML is not the only infection that MSers need to worry about. Other viral infections of the brain and eye can clearly cause major problems. I am aware of least one death from herpes encephalitis in an MSer on natalizumab. The presentation of encephalitis on natalizumab tends to be indolent and come over weeks to months. Why? The immune response to the causative infections agent is usually what bring encephalitis to the attention of the patient and clinician; if you prevent an immune response the virus replicates and does its damage more slowly. In fact in the fatality the team looking after the patient thought it was a brain tumour.”
Van et al. Progressive outer retinal necrosis in a multiple sclerosis patient on natalizumab. Neurology. 2015 May 26;84(21):2198-9. doi: 10.1212/WNL.0000000000001611.
A 54-year-old woman MSer, on natalizumab, reported 2 weeks of left eye redness and blurry vision, previously diagnosed as conjunctivitis. Visual acuity was 20/125. Funduscopy revealed progressive outer retinal necrosis (figure), a viral retinitis of immunocompromised patients that frequently causes vision loss. Sequential bilateral involvement is common. Etiologies include varicella zoster, herpes simplex, and rarely cytomegalovirus; aqueous PCR revealed varicella. Natalizumab was held. IV and intravitreal antivirals were administered. After repair of retinitis-induced retinal detachment and resolution of retinitis, visual acuity was 20/125. In immunocompromised patients with ocular symptoms, clinicians should consider infectious retinitis and obtain prompt funduscopic evaluation.