Differential diagnosis for a ring enhancing lesion in a patient with AIDS

Differential diagnosis for a ring enhancing lesion in a patient with AIDS

What is the differential diagnosis for a ring-enhancing lesion in a patient with autoimmune deficiency syndrome (AIDS)? 

While there are many causes of ring-enhancing lesions in both immunocompetent and HIV-infected individuals, the most important considerations in AIDS are toxoplasma, primary CNS lymphoma, tuberculoma, cryptococcoma, and bacterial abscess.

Metastases and primary CNS neoplasms should also be considered. The differential diagnosis may be altered based on the degree of immunosuppression.

Patients with CD4 counts >500/μL are more likely to have primary brain tumors or metastases, similar to immunocompetent hosts, whereas severely immunosuppressed patients with CD4 <200/μL are more likely to have opportunistic infections and AIDS-associated tumors.

What is the diagnostic algorithm for this type of patient? 

Lesions can be broadly divided into those with and without mass effect on imaging.

Those with mass effect include toxoplasma encephalitis, primary CNS lymphoma (PCNSL), and other infections such as bacterial abscesses, cryptococcoma, or syphilitic gummas.

Those without mass effect include progressive multifocal leukoencephalopathy (does not typically enhance but may be due to in context of immune reconstitution inflammatory syndrome (IRIS)), HIV encephalopathy (does not typically enhance but may in the context of immune reconstitution syndrome), and cytomegalovirus (CMV) encephalitis (typically with ventriculitis and ependymal enhancement). 

Patients without focal signs or significant mass effect should undergo lumbar puncture with cell counts and basic chemistries as well as polymer chain reaction (PCR) for JC virus, Epstein–Barr virus, cytomegalovirus, and Toxoplasma gondi (PCR and serology).

Workup should include blood cultures and full-body CT to assess for sources of bacterial infection or metastasis.

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