Infectious Disease · HIV/AIDS Opportunistic Infections
The facts most likely to be tested
Pneumocystis jirovecii pneumonia (PJP) presents with bilateral interstitial infiltrates and an elevated LDH in patients with a CD4 count < 200 cells/mm³.
Toxoplasma gondii encephalitis manifests as multiple ring-enhancing lesions on brain imaging and requires sulfadiazine and pyrimethamine for treatment.
Cryptococcal meningitis is characterized by an elevated opening pressure on lumbar puncture and is diagnosed via cryptococcal antigen testing in the CSF.
Cytomegalovirus (CMV) retinitis presents as hemorrhage and cotton-wool spots (pizza pie retinopathy) in patients with a CD4 count < 50 cells/mm³.
Mycobacterium avium complex (MAC) causes fever, night sweats, and weight loss and requires azithromycin prophylaxis when the CD4 count is < 50 cells/mm³.
Progressive multifocal leukoencephalopathy (PML) is caused by the JC virus and presents with non-enhancing white matter lesions without mass effect on MRI.
Esophageal candidiasis is an AIDS-defining illness that presents with odynophagia and is treated empirically with fluconazole.
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A 34-year-old male with a history of untreated HIV presents with a 3-week history of progressive headache, confusion, and low-grade fever. Physical examination reveals mild left-sided hemiparesis. A CT scan of the head shows multiple ring-enhancing lesions with surrounding edema. His most recent CD4 count was 45 cells/mm³.
What is the most appropriate initial pharmacologic treatment?
Pyrimethamine and sulfadiazine
The patient's presentation of multiple ring-enhancing lesions in the setting of severe immunosuppression is classic for Toxoplasma gondii encephalitis, which is treated with pyrimethamine and sulfadiazine.
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Etiology / Epidemiology
Opportunistic infections occur when CD4 count < 200 cells/µL due to progressive immune exhaustion.
Clinical Manifestations
Presentation varies by pathogen; Pneumocystis presents with exertional dyspnea and ground-glass opacities.
Diagnosis
Diagnosis requires CD4 count monitoring and pathogen-specific PCR or biopsy.
Treatment
Prophylaxis is mandatory: Trimethoprim-sulfamethoxazole is the gold standard for multiple infections.
Prognosis
Prognosis is tied to ART adherence and maintaining CD4 > 200 to prevent mortality.
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Epidemiology & Etiology
Infections arise when the immune system fails to contain latent or environmental pathogens. Risk is stratified by CD4 count thresholds. Primary prophylaxis is indicated for patients with advanced immunosuppression.
Pertinent Anatomy
The lungs are the primary site for Pneumocystis jirovecii. The central nervous system is the target for Toxoplasma gondii and Cryptococcus neoformans.
Pathophysiology
HIV destroys CD4+ T-lymphocytes, leading to a loss of cell-mediated immunity. This allows reactivation of latent infections or susceptibility to low-virulence organisms. The clinical syndrome is defined by the specific pathogen's predilection for the immunocompromised host.
Clinical Manifestations
PCP presents with dry cough and hypoxemia. Toxoplasmosis manifests as focal neurologic deficits and ring-enhancing lesions. Altered mental status in HIV patients requires immediate neuroimaging to rule out space-occupying lesions.
Diagnosis
The CD4 count is the primary diagnostic tool for risk stratification. PCR is the gold standard for viral and fungal detection. Bronchoalveolar lavage is the definitive test for pulmonary opportunistic infections.
Treatment
Trimethoprim-sulfamethoxazole is the first-line agent for both treatment and prophylaxis of PCP and toxoplasmosis. Sulfa allergy necessitates desensitization or alternative agents like atovaquone. ART must be initiated to restore immune function.
Prognosis
Mortality is highest in patients with CD4 < 50. Long-term survival depends on viral load suppression and adherence to prophylactic regimens.
Differential Diagnosis
Pneumocystis jirovecii: exertional dyspnea with normal chest exam
Toxoplasmosis: multiple ring-enhancing lesions on MRI
Cryptococcal meningitis: elevated opening pressure on lumbar puncture
CMV retinitis: pizza pie appearance on fundoscopy
Mycobacterium avium complex: CD4 < 50 and systemic wasting