Misdiagnosis of multidrug-resistant tuberculosis possibly due to laboratory-related errors
A. T. Nitta, P. T. Davidson, M. L. de Koning and R. J. Kilman
Tuberculosis Control, Los Angeles County Department of Health Services, Public Health Programs and Services, Los Angeles, Calif., USA.
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.
