Tuberculin skin test overestimates tuberculosis hypersensitivity in adult patients with psoriasis.

BACKGROUND

Tuberculin skin testing (TST) is still the reference method for the diagnosis of latent tuberculosis infection (LTBI).

OBJECTIVE

To evaluate the effect of psoriasis on TST.

METHODS

Comparison of TST results of consecutive dermatology (n = 91) and internal medicine (n = 615) inpatients. TST was uniformly ordered, performed and evaluated according to the Mantoux method using purified protein derivative.

RESULTS

(a) Significantly larger TST indurations were measured in dermatology (median: 7 mm) compared to internal medicine inpatients (median: <1 mm; p < 0.0001). More dermatology inpatients showed 'positive' (>5 mm) and 'strongly positive' (>or=15 mm) TST results (53 vs. 29% and 22 vs. 13%, respectively). (b) Among dermatology inpatients, the TST reactions were significantly larger (p < 0.01) in psoriatics (n = 28) compared to the remaining patients (n = 63). (c) In psoriatics, the TST correlated positively with the psoriasis area and severity index score (p = 0.015).

CONCLUSION

Overt psoriasis is associated with increased TST measurements. This observation is suggestive of a possible overtreatment of these patients for LTBI.