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.