HIV/AIDS (pulmonary and thoracic manifestations)
Pulmonary and thoracic manifestations of HIV/AIDS are a major contributor to morbidity and mortality related to the disease. The differential in an HIV patient with a chest complaint is broad. Infectious causes are the most common, however, neoplasms, lymphoma and interstitial pneumonia also play a significant role.
A systematic approach that takes into account the imaging findings, the severity of immunosuppression (CD4 count as a surrogate marker) and the clinical presentation should narrow the differential.
Some groups of HIV patients are predisposed to certain associated conditions. For example, lymphocytic interstitial pneumonitis is considerably more common in pediatric patients. Kaposi sarcoma is seen predominantly in the homosexual male population.
The type and onset of respiratory complaint may narrow the differential diagnosis.
Acute onset of febrile illness favors bacterial infection. The presence of a productive cough also favors pyogenic infection and points away from pneumocystis pneumonia.
An insidious onset of symptoms is more typical of tuberculous, non-tuberculous mycobacterial, or fungal infection. Persistent symptoms that do not respond to therapy raise suspicion of a neoplastic process.
The number of CD4 lymphocytes in the blood determines possible organisms responsible for pulmonary infection.
- >200 cells/mm3: all patients with HIV are at an increased risk of bacterial infections and TB, the risk increases further as CD4 count drops
- <200 cells/mm3: also susceptible to PCP, atypical mycobacteria
- <100 cells/mm3: also susceptible to CMV, disseminated fungal and mycobacterial infections
The spectrum of thoracic pathologies include 6:
- bacterial pneumonia
- features secondary to Mycobacterium tuberculosis
- human herpesvirus 8 (HHV-8)-related diseases
- other infections
- other conditions
Imaging appearances of patients with AIDS-related chest conditions are protean and often non-specific. A pattern-based approach is suggested for narrowing the differential diagnosis.
A chest x-ray is generally the initial examination, however, a CT is often warranted for characterization.
Normal chest x-ray
The chest x-ray is not infrequently normal in an HIV patient presenting with a respiratory complaint. Consider:
- upper respiratory tract infection: common in HIV
- radiographically-occult infections such as viral or bacterial bronchiolitis
- imaging patterns that may be difficult to see on plain x-ray, e.g. ground-glass opacity with pneumocystis pneumonia
Focal airspace opacity
Bacterial infection is most likely, of which Streptococcus pneumoniae is most common. In the severely immunosuppressed, consider also tuberculosis. A non-resolving airspace opacity may be due to malignancy.
Multifocal airspace opacity
A multifocal bacterial infection is again most likely.
When the opacities are nodular consider fungal infection, mycobacteria and Nocardia asteroides.
Pneumocystis pneumonia is a common cause of ground-glass opacity in the immunocompromised host: although incidence has decreased with the advent of prophylactic therapy and HAART (highly active antiretroviral therapy). Look for the typical perihilar distribution. There may be a crazy-paving appearance.
Other infectious differentials include viral and atypical bacterial infections. In the severely immunocompromised (CD4 count <100 cells/mm3), consider CMV pneumonia.
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