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JC virus (Progressive multifocal leukoencephalopathy)

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JC virus (Progressive multifocal leukoencephalopathy)

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JC virus (Progressive multifocal leukoencephalopathy)

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A 38-year-old woman is brought to the emergency department due to progressively worsening confusion and inability to walk. She lives at home with her partner, who states that over the past week the patient has had worsening memory and trouble moving the right side of her body. The patient was diagnosed with HIV infection 3 years ago but has been non-compliant with antiretroviral therapy. Temperature is 37.0°C (98.6°F), pulse is 92/min, respirations are 13/min, and blood pressure is 125/72 mmHg. Physical examination reveals oral thrush. The patient is not oriented to time, place, or person. Neurological examination reveals right-sided hyperreflexia and upgoing plantar reflex. CD4 count is 90/mm3. MRI shows multiple, nonenhancing white matter lesions. Reactivation of a pathogen from which of the following locations is most likely responsible for this patient’s current symptoms?  

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In progressive multifocal leukoencephalopathy, progressive means that the disease worsens over time, multifocal means the disease affects multiple locations, leuko refers to white, and encephalopathy refers to a disease of the brain.

So progressive multifocal leukoencephalopathy or simply PML, is a disease of the white matter of the brain that affects multiple locations and worsens over time.

If we look at a cross section of the brain, it can be divided into two areas: the outermost area is the grey matter, which is made up of neuron cell bodies, and the innermost area is the white matter, which is made up of the axons that come off of the neuron cell bodies.

The axons transmit electrical impulses to the next neuron in the series.

The axons are surrounded by a fatty protective sheath called myelin that helps increase the speed at which electrical impulses are sent.

Myelin is produced by a special type of cells called oligodendrocytes.

The cause of progressive multifocal leukoencephalopathy is the John Cunningham virus, or simply JC virus, named after the first patient in whom the virus was identified.

JC virus is a non-enveloped virus with closed circular double-stranded DNA genome.

It’s thought that the virus is transmitted from person to person through the respiratory and gastrointestinal tract, and that it then moves through the bloodstream and eventually reaches kidney epithelial cells.

JC virus enters these kidney cells and starts replicating, but the cytotoxic CD8+ T cells of our immune system keep the virus in check by killing any cell that has replicating JV virus.

So to be clear, the virus is not eliminated, but instead it remains latent in the kidneys, meaning that it isn’t dividing and causing disease.

And It turns out that the vast majority of the population is infected by JC virus - that might include you!

Most people with a healthy immune system are able to keep JC virus in the latent phase in the kidney epithelial cells for their entire life. But things can change if the immune system gets weakened.

This can happen for various reasons, like an HIV-infected individual who loses T cells, or individuals taking immunosuppressive medications like monoclonal antibodies such as natalizumab, which is typically used to treat multiple sclerosis, and rituximab, which is used to treat various cancers and autoimmune diseases.

Summary

Progressive multifocal leukoencephalopathy (PML) is a rare, often fatal demyelinating disease of the brain, caused by JC virus. JC virus is a non-enveloped, double-stranded DNA virus that can be found latent and harmless in most adults.

However, in people with weakened immune systems, the virus can cause PML, in which the white matter in the brain gets destroyed, leading to progressive and irreversible axon demyelination that presents with motor and cognitive neurological symptoms

There is no specific treatment for PML and it is usually fatal. However, some people with PML may improve with treatment for their underlying condition (e.g., HIV/AIDS).