Mr. P, age 67, presents to the clinic with vision changes and memory loss following a fall in his home due to limb weakness. Six years ago, his care team diagnosed him with rheumatoid arthritis (RA). Mr. P’s current medication regimen includes methotrexate 20 mg once weekly and etanercept 50 mg once weekly, and he has been stable on this plan for 3 years. Mr. P also was recently diagnosed with major depressive disorder (MDD), but has not yet started treatment. Following a complete workup, an MRI of Mr. P’s brain revealed white matter demyelination. Due to these findings, he is scheduled for a brain biopsy, which confirms a diagnosis of progressive multifocal leukoencephalopathy (PML).
PML is a demyelinating disease of the central nervous system caused by the John Cunningham virus (JCV), or JC polyomavirus, named for the first patient identified to have contracted the virus.1 Asymptomatic infection of JCV often occurs in childhood, and antibodies are found in ≤70% of healthy adults. In most individuals, JCV remains latent in the kidneys and lymphoid organs, but immunosuppression can cause it to reactivate.2
JCV infects oligodendrocytes, astrocytes, and neurons, which results in white matter demyelination. Due to this demyelination, individuals can experience visual field defects, speech disturbances, ataxia, paresthesia, and cognitive impairments.2 Limb weakness presents in 60% of patients with PML, visual disturbances in 20%, and gait disturbances in 65%.3 Progression of these symptoms can lead to a more severe clinical presentation, including focal seizures in ≤10% of patients, and the mortality rate is 30% to 50%.3 Patients with comorbid HIV have a mortality rate ≤90%.2
Currently, there are no biomarkers that can identify PML in its early stages. A PML diagnosis is typically based on the patient’s clinical presentation, radiological imaging, and detection of JCV DNA. A brain biopsy is the gold standard for PML diagnosis.1
Interestingly, data suggest that glial cells harboring JCV in the brain express receptors for serotonin and dopamine.4 Researchers pinpointed 5HT2A receptors as JCV entry points into cells, and theorized that medications competing for binding, such as certain psychotropic agents, might decrease JCV entry. Cells lacking the 5HT2A receptor have shown immunity to JCV infection and the ability of cells to be infected was restored through transfection of 5HT2A receptors.4
Immunosuppressant medications can cause PML
PML was initially seen in individuals with conditions that cause immunosuppression, such as malignancies and HIV. However, “drug-induced PML” refers to cases in which drug-induced immunosuppression creates an environment that allows JCV to reactivate and disseminate back into the CNS.4 It is important to emphasize that drug-induced PML is a very rare effect of certain immunosuppressant medications. Medications that can weaken the immune system include glucocorticoids, monoclonal antibodies, alkylating agents, purine analogues, antimetabolites, and immunosuppressants (Table).1
These medications are used to treat conditions such as multiple sclerosis, RA, psoriatic arthritis, and lupus. Although drug-induced PML can result from the use of any of these agents, the highest incidence (1%) is found with natalizumab. Rates of incidence with other agents are either unknown or as low as .002%.1 Evidence suggests that the risk for PML increases with the duration of therapy.5
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