Clinical Features, Treatment and Outcomes of Dogs With Psoriasiform Lichenoid Dermatosis Associated With Calcineurin Inhibitor Therapy.

Background: Psoriasiform lichenoid dermatosis (PLD) is a rare lesion in dogs receiving calcineurin inhibitors, associated with staphylococcal infection.

Objectives: To define the clinical features of dogs with a histopathologic diagnosis of PLD.

Results: Twenty-eight dogs were included in this retrospective study. PLD was focal (4/28), multifocal (17/28) or regional/generalised (7/28). Twenty-seven of 28 dogs received a calcineurin inhibitor with a median time to lesion onset of 6 months (1-24 months). Twenty-three of 28 dogs received ciclosporin (ciclosporin alone: 15/23; ciclosporin with ketoconazole: 7/23). Formulations included generic modified ciclosporin (12/23), brand-name modified ciclosporin (7/23), compounded modified ciclosporin (1/23) or unknown formulation (3/22). Four dogs had gingival hyperplasia or paw-pad hyperkeratosis. Four dogs received topical tacrolimus. No breed or sex predilection was found. The median age of onset was 7 years (3-12 years). In 22/28 dogs, bacteria were seen on lesional cytology, and Staphylococcus pseudintermedius was isolated with bacterial culture from nine dogs. Short-read whole genome sequencing was performed on three isolates. Most dogs received antimicrobials before (14/28) and/or after diagnosis (22/28 dogs).

Outcomes/clinical relevance: PLD occurs in adult dogs irrespective of breed with varied forms of calcineurin inhibitors. Twenty of 28 dogs achieved > 50% improvement or complete (100%) lesion resolution after topical and/or systemic antimicrobial therapy and discontinuation with or without dose reduction of the calcineurin inhibitor.