Psoriasis plaque test

Synonym(s)

Microplaque Assay; PPT

Method for testing the topical, antipsoriatic potency of various substances.

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Dermatology

Rare, acute, rarely chronic, neutrophilic pustulosis on palmae and/or plantae of unexplained etiology (infe...

First, selection of chronic inpatient plaques (mainly in the extremities) without inflammatory marginal activity (lesions should remain untreated before testing).
If there was a pre-treatment, a 14-day washout phase should be observed with topical applications and a 1-3-month washout phase with systemic treatment (corresponding to the half-life).
Then separate assessment of the severity of the individual symptoms (redness, scaling, infiltration).
Evaluation according to the following scheme (0 = not present, 1 = mild, 2 = moderate, 3 = severe, 4 = very severe).
Addition of each score according to individual symptoms.
Sum corresponds to the initial activity (100%).
Subsequently, daily application of the test substance (with positive and negative controls!), either open or occlusive (e.g. with Finn-Chambers).
Daily careful washing of the test areas and if occlusive, renewal of the Finn-Chambers.
Daily determination of the score for each symptom.
Repeating the procedure for a total of 5-15 days (depending on pharmacological properties).
The final score corresponds to the so-called residual activity (compared to the initial activity).

Modifications exist with regard to the number of test fields, size of the areas, form of application, frequency of application, total duration, combination with systemic therapy, etc.
Due to the heterogeneity of psoriatic skin lesions, the test areas should rotate from patient to patient. Topographic influences should be minimized.
The evaluation of the test areas should not be performed immediately after washing, but with a latency of one hour. Scaling, for example, is not correctly detected after washing.
Skin irritation caused by plasters should be excluded.