Suppurative Malassezia Otitis Externa: Clinical Features, Treatment, and Preliminary Isolate Identification.

Background: Suppurative Malassezia otitis externa (SMO) is a rare, severe presentation of Malassezia otitis (MO) sparsely reported in the literature.

Hypothesis/objectives: The primary objective of this study was to describe the clinical presentation, diagnostic findings, treatment, and prognosis of SMO. A secondary objective was to speciate available SMO isolates, as this phenotype may be caused by different Malassezia species.

Animals: Nine client-owned dogs with SMO.

Materials and methods: A retrospective study of medical records from nine dogs with SMO diagnosed at an academic referral hospital from 2022 to 2024. Three SMO and 10 MO isolates from poodle-crosses were speciated with matrix-assisted laser desorption and ionisation time-of-flight mass spectrometry (MALDI-TOF MS).

Results: Young (average 1-year-old), male (67%), poodle or poodle-crosses (67%; six of nine dogs) were most often affected. Clinical presentation included unilateral otitis externa (77%; seven of nine dogs) with dark brown mucoid discharge, canal ulceration, erythema and glandular hyperplastic changes (100%). Cytological findings included yeast, neutrophils, and extracellular material suggestive of biofilm (100%). Prior otic treatment was primarily misdirected towards Pseudomonas otitis. Malassezia pachydermatis was identified in two SMO isolates and half of the MO isolates. Prednisone (0.5-1 mg/kg/day) per os daily tapered over 1 month plus daily otic orbifloxacin, mometasone furoate monohydrate and posaconazole (Posatex; Merck Animal Health) achieved complete resolution in 83% of affected ears without an anaesthetised otic lavage. At the time of writing, there was no known recurrence of any case within at least 6 months of treatment.

Conclusions and clinical relevance: SMO is a phenotypically severe presentation of MO clinically mimicking suppurative bacterial otitis. Young, male poodle-crosses are commonly affected. Ear canal hair plucking is likely to incite severe primary inflammation before SMO development.