Immune reconstitution inflammatory syndrome (IRIS) complicating PML

Case contributed by Dr Alexandra Stanislavsky


Patient with HIV, not on anti-retroviral therapy, presents with ataxia and dysarthria. CD4+ count 70 cells/mm3.

Patient Data

Age: 40 years
Gender: Male

Bilateral cerebellar patchy white matter T2w signal hyperintensity, without enhancement, diffusion restriction or mass effect.


2 weeks later. Patient commenced on antiretroviral therapy, but symptoms deteriorating. CD4+ 200 cells/mm3.

The area of abnormal T2 hyperintensity within the cerebellar hemispheres has now increased, now also involving the left middle cerebellar peduncle. There is new enhancement corresponding to the edge of the abnormal T2 signal.


Another 2 weeks later. Following corticosteriod therapy.

Persistent cerebellar signal abnormality, but there is no longer any enhancement.

Case Discussion

This case demonstrates the imaging appearance of immune reconstitution inflammatory syndrome (IRIS) complicating progressive multifocal leukoencephalopathy (PML) in an AIDS patient with a low CD4 count.

The first scan demonstrated background PML changes. The progressive appearance and new enhancement seen on the second MRI, particularly given the clinical setting of worsening symptoms after initiation of therapy, is consistent with IRIS. The subsequent improvement following treatment with steroids (on the third followup MRI) supports this.

IRIS is a phenomenon of paradoxic worsening of clinical and/or radiological inflammatory illness which is sometimes seen in AIDS patients who are commenced on HAART (Highly Active Anti Retroviral Therapy), usually in the setting of low CD4 count/high viral load.

It is thought to occur due to restoration of the previously suppressed inflammatory immune response, and has been described in patients with various AIDS related illnesses, including TB, cryptococcus, CMV, Kaposi’s sarcoma – as well as PML.

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Case information

rID: 16230
Published: 1st Jan 2012
Last edited: 13th Aug 2019
Inclusion in quiz mode: Included

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