What is the appropriate duration of a therapeutic trial in cutaneous tuberculosis? Further observations

Background: Laboratory tests for the diagnosis of cutaneous tuberculosis lack adequate sensitivity and specificity and a trial of therapy is often used as a diagnostic test in difficult cases. However, the duration for which the trial should be undertaken is not clearly defined. Our previous study indicated that one month of therapy was adequate to detect a clinical response to treatment. However, about half the patients first reported after one month of treatment, some much later.
Method: We therefore analysed the treatment records of 107 patients who received four-drug, short course, antitubercular therapy for a diagnosis of cutaneous tuberculosis in our hospital and who were asked to return for follow-up at biweekly intervals in the first month of treatment.
Result: Twenty-one patients did not return for any follow-up visit, nine patients did not respond to treatment and treatment was stopped in one patient. Of the remaining 76 patients, 72 patients were recorded to have distinct clinical improvement within five weeks of starting treatment while only four patients showed improvement after 60-123 (8-17 weeks) days of therapy.
Conclusion: These findings indicate that five weeks appears to be an adequate duration of a therapeutic trial in patients suspected to have cutaneous tuberculosis, with the exception of tuberculids and patients showing minimal clinical activity before treatment. Patients who have not responded by this time are unlikely to do so with further treatment and should have their diagnosis reviewed.