Posting #7 - Effect of HIV on Diagnosis of TB disease

Diagnosis of TB in HIV+ Patients
Effect of HIV on TB

The main effect of HIV on TB

• Cell-mediated immunity is the host's main defense against TB
• CD4+ cells are a key part of cell-mediated immunity
• CD4+ are depleted by HIV infection
• HIV reduces the host's ability to fight off primary infection

Key question

• What is the Patient's CD4 cell count?

CD4 cell count > 200 cells/μL

Clinical presentation is similar to HIV seronegative patients

• Primarily pulmonary TB
• Nights sweats
• Fever
• Weight loss
• Fatigue/malaise
• Cough w/sputum

Diagnostics are similar to HIV seronegative patients

• PPD > 5mm induration is positive
• Acid-fast staining: AFB has high sensitivity, low specificity (high false negatives)
• Chest X-rays: pulmonary cavitation in upper lung fields
• Sputum culture is still gold standard

CD4 cell count

• Unexplained fevers
• Lymphadenopathy, especially in extrathoracic nodes (cervical & axillary)
• Some will still present as typical seronegative patient

Diagnostics are similar to primary infection

• PPD: high false negatives d/t anergy
• QFT-G: high number of indeterminate results
• Acid-fast staining: often negative
• Sputum culture: Still the best test, highest sensitivity and specificity. Be sure to do the 3 separate sputum sample. Repeat test if TB is still suspected!

Chest Radiographs

• may be normal
• may have non-cavitatory infiltrates in middle or lower lung fields, intrathoracic lymphadenopathy consistent with primary TB
• may be typical of TB disease in seronegative patients

Clinical presentation is more likely to be a disseminated/extrapulmonary tuberculosis

• TB can present anywhere, although lymph nodes and pleural space is most likely
• Test serum and urine cultures - good test for disseminated TB
• Abdominal/Pericardial TB
• Lymph node aspiration – swelling of nodes
• Head CT/Lumbar puncture for CSF - meningitis
• Sample sites if relevant to S/Sx

Summary

• TB can be sub-clinical
• Manifested as indeterminate symptoms
• Has higher mortality
• More difficult to diagnose in TB endemic areas
• Complicated by limited resources
• Low cost effective diagnostic tool is still needed
• High cost effective diagnostic tool isn't available yet.

References

American Thoracic Society. (2000). Diagnostic Standards and Classification of Tuberculosis in Adults and Children. American Journal of Respiratory and Critical Care Medicine, 161, 1376–1395.

El-Sadr, W. M., & Tsiouris, S. J. (2008). HIV-associated tuberculosis: diagnostic and treatment challenges. Seminars in Respiratory and Critical Care Medicine, 29(5), 525-531. doi: 10.1055/s-0028-1085703

Maartens, G. (2009). Clinical features and diagnosis of tuberculosis in HIV-infected patients. Retrieved November 24, 2009, from http://www.uptodate.com.offcampus.lib.washington.edu/online/content/topic.do?topicKey=tubercul/7537&selectedTitle=1%7E150&source=search_result

Post, F. A., Wood, R., & Pillay, G. P. (1995). Pulmonary tuberculosis in HIV infection: radiographic appearance is related to CD4+ T-lymphocyte count. Tubercle and Lung Disease: The Official Journal of the International Union Against Tuberculosis and Lung Disease, 76(6), 518-521.