Clinical Characteristics of Hair Cycle Arrest in Toy Poodles: A Retrospective Comparison With Pomeranians

BACKGROUND: Hair cycle arrest (HCA), known as alopecia X, is an alopecia disorder most commonly reported in Nordic breeds-particularly Pomeranians. Toy poodles (TPs) also are frequently affected, yet their clinical characteristics have not been reviewed systematically. OBJECTIVES: The aim of this retrospective case series was to compare the clinical characteristics of HCA in TPs and Pomeranians. MATERIALS AND METHODS: Medical records of client-owned dogs diagnosed with HCA between 2018 and 2024 were reviewed. Signalment, including age of onset and age at diagnosis, clinical features, skin barrier function (transepidermal water loss [TEWL], stratum corneum hydration [SCH]) and treatment outcomes were analysed. RESULTS: Fifty dogs (19 TPs, 31 Pomeranians) met the inclusion criteria. TPs were significantly older than Pomeranians both at disease onset and at the first presentation (p = 0.003 and p = 0.001, respectively). Both breeds exhibited similar bilateral symmetrical alopecia presentations; however, Pomeranians mainly presented with a single alopecic site, while nearly half of the TPs had multiple affected sites (p = 0.032). Pruritus and superficial pyoderma were common in both breeds. TEWL and SCH values frequently deviated from reference ranges (increased TEWL and decreased SCH), indicating impaired skin barrier function. TEWL was significantly higher in TPs with pyoderma than in those without (p = 0.025). Regarding outcomes, > 70% of patients showed partial or complete regrowth, despite various treatment regimens. CONCLUSIONS AND CLINICAL RELEVANCE: HCA in TPs closely resembles that in Pomeranians, despite genetic divergence, suggesting a conserved pathogenesis across their breeds. Frequent pruritus and pyoderma, together with abnormal TEWL and SCH, indicate secondary skin barrier dysfunction. Clinical management should address both hair regrowth and restoration of skin barrier function.