Abstract:

Periodic Acid-Schiff (PAS) stain is frequently used in dermatopathology. Studies of PAS on skin biopsies have shown that the stain may be positive for fungus even when there is not clinical suspicion for fungus. These studies are mostly retrospective with small sample sizes. Current appropriate use criteria support using PAS with non-specific clinical and pathologic findings that could represent dermatophytosis. Ordering PAS incurs expense, raising concerns about cost-effectiveness. Current practice in our lab, like others, is to order PAS before tissue processing (‘pre-order’) for any specimen that includes an inflammatory dermatosis or infection on the clinical differential. We sought to assess if clinical differential diagnosis could direct pre-ordering of PAS using a quality improvement approach. Current state analysis involved retrospective review of a 12-month period of all biopsies for which PAS was pre-ordered. Clinical differential diagnoses and PAS positivity were collected. PAS was pre-ordered on 616 cases of which eczematous (n=250, 40.6%), papulosquamous (n=226, 36.7%), urticaria, erythema and purpura (n=182, 29.5%), lymphoproliferative disorders (n=172, 27.9%), and neoplasms (n=113, 18.3%) were the most common diagnoses included on the clinical differential. Fifteen cases (2.4%) were PAS-positive, 8 showed non-infectious fungi (1.3%), and 595 were PAS negative. Clinical suspicion of fungus was significantly associated with PAS positivity. Inclusion of lymphoproliferative disorders on the differential was significantly associated with negative PAS (p<0.05). Clinical differential including infection (p<0.05), vesiculobullous (p<0.05), and superficial mycoses (p<0.05) were significantly associated with positive PAS. Based on these data, we will trial an intervention using more selective criteria for pre-ordering PAS while assessing cost implications. PAS positivity rate will be reassessed. These data will be available at the ASDP annual meeting.

Financial Disclosure:
No current or relevant financial relationships exist.

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Howa Yeung, MD, MSc