Molecular analysis of sarcoidosis lymph nodes for microorganisms: a case–control study with clinical correlates

Robinson, Lary A; Smith, Prudence; SenGupta, Dhruba J; Prentice, Jennifer L; Sandin, Ramon L

Many pathogenic microorganisms such as Mycobacterium leprae (leprosy) or coronaviruses (severe acute respiratory syndrome) cannot be grown directly in culture or they are very slow growing or difficult to culture such asTropheryma whippelii (Whipple's disease) . 5, 19 In these instances, detection and identification rely on molecular mechanisms such PCR used in this study. Nevertheless, the molecular approach has distinct limitations including possible falsepositive results secondary to contaminated PCR reagents, the paraffin imbedding process, or post-embedding handling and processing of the paraffin block. However in our study, thirty control lymph nodes were processed in an identical manner and bacterial DNA was detected in only 2/30 (6.6%), significantly less than the sarcoidosis nodes (36.7%, p = 0.00516), suggesting that contamination is unlikely to account for the findings. 16 Of note, the only 3 sarcoidosis lymph nodes positive for mycobacteria in our study were less than 3 years old when evaluated by PCR. Had we used fresh lymph node tissue like Drake and associates 16 who found 60% PCR positive for mycobacteria species, there may have been a much higher rate of positive bacterial DNA results (particularly mycobacteria) in our study.