Misdiagnosis of multidrug-resistant tuberculosis possibly due to laboratory-related errors

Objective.-To describe 9 cases where a misdiagnosis of multidrug-resistant tuberculosis (MDR TB) was made, possibly due to laboratory-related errors. Design.-Case series. Setting.-Public and private hospitals, outpatient clinics, and mycobacteriology laboratories serving those institutions in Los Angeles County, Calif. Patients.-Consecutive sample of 70 patients diagnosed with MDR TB who were identified between August 1993 and August 1994 by the Multidrug-Resistant Unit within TB Control in Los Angeles County. Outcome Measure.-Detection of laboratory-related diagnostic errors. Results.-Pulmonary MDR TB was misdiagnosed in 9 (13%) of 70 patients. Reasons why the diagnoses appeared to be erroneous are as follows. growth of MDR TB from an old tuberculous lesion in a patient who was never treated for TB and whose diagnosis predated anti-TB drugs (1 case), documented contamination with Mycobacterium avium complex (1 case), suspected cross-contamination (1 case), suspected specimen mislabeling (1 case), successful treatment using drugs to which the isolate was reportedly resistant (4 cases), discrepant susceptibility test results on additional sputum specimens submitted by the patient (2 cases), and no clinical evidence of TB (3 cases). Conclusions.-These cases emphasize the diagnostic errors that can occur if mycobacterial susceptibility results are not correlated with all clinical data including other laboratory results for a given patient. We conclude that susceptibility results alone are not enough to dictate treatment, and that careful clinical correlation is necessary in making the diagnosis of MDR TB.