26th June 2023

Immunosuppressed Patients

Immunosuppressed states can significantly increase the risk of several brain lesions, outlined in this section. A brief understanding of these is important to be able to consider these diagnoses in clinical practice so that potential brain-sparing and life-saving treatments can be initiated early; they are also a common topic in MRCP questions.

Toxoplasmosis

Toxoplasmosis is caused by infection with the parasite Toxoplasma gondii, which is classically spread through infected meat that is inadequately cooked or through contact with oocysts from cat faeces.

Infection may cause symptoms such as headache, confusion, unsteady gait, seizures, and fevers in the immunosuppressed. Contrast CT features of cerebral toxoplasmosis include multiple ring-enhancing hypodense lesions in the basal ganglia and corticomedullary junction. Occasional mass effect and midline shift may be present due to the increasing size of the lesions. The treatment of acute toxoplasmosis in immunocompromised patients is with sulfadiazine and pyrimethamine. Prophylaxis with co-trimoxazole may be given to HIV-positive patients with low CD4+ counts.

Toxoplasmosis on MRI.

Image Source: Wikimedia Commons (2019). BrainToxoplasmosis MRI 4 11, Licensed under a creative commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:BrainToxoplasmosis_MRI_4_11.png (Accessed on: 30 January 2023).

Primary CNS lymphoma

Primary CNS lymphoma (PCNSL) is a rare tumour confined to the central nervous system with no evidence of systemic spread. The risk of PCNSL is much higher in immunocompromised patients, particularly those with HIV/AIDS. PCNSL usually develops from B-cell lymphocytes; the most common subtype is diffuse large B-cell lymphoma and is associated with prior Epstein-Barr virus infection. The symptoms can include those of increased intracranial pressure (e.g. headache, vomiting), diplopia, behavioural changes, seizures, and focal neurological signs.

Radiological findings vary from well-circumscribed, solid, homogenous lesions in immunocompetent individuals, to peripheral enhancement with central necrosis of the lesion and vasogenic oedema in immunodeficiency-related CNS lymphomas. The majority of PCNSLs are solitary lesions, however, it can also present with multiple lesions.

Treatment options include steroids (to reduce the oedema surrounding the tumour), chemotherapy and radiotherapy. Neurosurgical resection may be considered for low grade tumours.

Primary CNS lymphoma on MRI brain

Image Source: Wikimedia Commons (2007). Tumor PrimaryCNSLymphoma T1Axial, Licensed under a creative commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:Tumor_PrimaryCNSLymphoma_T1Axial.JPG (Accessed on: 30 January 2023).

Progressive multifocal leukoencephalopathy

Progressive multifocal leukoencephalopathy (PML) is a manifestation of infection with the JC virus in immunocompromised individuals. It causes progressive, widespread demyelination due to JC virus infection of oligodendrocytes within the brain. The symptoms are slow and insidious, including behavioural changes, speech, motor, and visual impairment. It almost exclusively affects those who are severely immunosuppressed, however, increased incidence has been associated with the introduction of immunosuppressant monoclonal antibody therapies such as natalizumab, efalizumab, and rituximab for the treatment of various autoimmune disorders.

CT head can show single or multiple multifocal lesions which usually do not enhance. An MRI is the gold-standard imaging choice, revealing high-signal demyelinating white matter lesions.

Prognosis is very poor, associated with neurological disability and if left untreated, is usually fatal within one year. Treatment focuses on reversing the immune deficiency of the patient to slow or stop the progression of PML. In patients with HIV, treatment involves starting antiretroviral therapies (ART) to increase the patient’s CD4+ count to assist in halting the progression of the infection.

Progressive Multifocal Leukoencephalopathy on MRI brain.

Image Source: Wikimedia Commons (2008). Progressive multifocal leukoencephalopathy 002, Licensed under a creative commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:Progressive_multifocal_leukoencephalopathy_002.jpg (Accessed on: 30 January 2023).