Is tuberculous lymphadenitis over-diagnosed in Ethiopia? Comparative performance of diagnostic tests for mycobacterial lymphadenitis in a high-burden country.

Ethiopia reports the third highest number of extrapulmonary TB cases globally, most of which are lymph node TB (TBLN). We investigated the performance of the available diagnostic tests for TBLN. Fine needle aspirate (FNA) and excision biopsy samples from affected lymph nodes were collected from 150 consenting patients with suspected TBLN visiting regional hospitals in Ethiopia. The sensitivity, specificity, positive (PPV) and negative predictive value (NPV) of histopathology against culture as reference was 92%, 88%, 97% and 77% and of FNA cytology (FNAC) 76%, 88%, 100% and 55%, respectively. Naked eye examination of FNA had 67% sensitivity and 64% specificity. HIV coinfection did not diminish the performance of macroscopic examination, Ziehl-Neelsen stain, histology or cytology examinations. When any positive result in ZN, histopathology or culture was considered confirmatory, clinical diagnosis could be confirmed in 85% of the patients, suggesting that TBLN is over-diagnosed in up to 15% of cases. With combined criteria as reference standard, the sensitivity, specificity, PPV and NPV of FNAC was 72%, 100%, 100% and 55%, respectively. FNAC is a practical tool that can improve the diagnosis of TBLN in high-burden settings. Over-diagnosis alone cannot explain the high burden of LNTB in Ethiopia.