Hair fragility (trichorrhexis nodosa) in alopecic Pomeranian dogs.

Background: While alopecia associated with hair cycle arrest (HCA, Alopecia X) is well-recognised in Pomeranian dogs, the authors are unaware of reports of concurrent hair fragility.

Hypothesis/objectives: Following the observation of frequent hair shaft abnormalities in alopecic Pomeranians, we hypothesised that hair fragility events would be more frequent in dogs with a phenotype of HCA when compared to dogs with normal coats.

Animals: Eight alopecic Pomeranian dogs or crosses with a phenotype of HCA and 36 unaffected Pomeranians with owner-reported normal hair coats.

Materials and methods: All affected dogs underwent dermatological examination and clinicopathological evaluations. Hair samples, plucked from affected areas or obtained by brushing from unaffected dogs, were examined microscopically for structural abnormalities. Hair fragility events were characterised as trichorrhexis nodosa (TN) or longitudinal splits and were expressed per 10 mg of hair. A reference interval was calculated from the number of hair fragility events in the samples from unaffected dogs.

Results: The upper reference limit (with 90% confidence) from samples of 35 unaffected Pomeranians (one outlier excluded) was 9.75 hair fragility events per 10 mg of hair. The median (range) of fragility events in eight dogs with a phenotype of HCA was 66.0 (30.2-166.7) per 10 mg of hair.

Conclusions and clinical relevance: Clinicians should routinely perform trichography in Pomeranians with HCA because abundant hair abnormalities, particularly TN, may contribute to poor hair coat quality. Further studies are required to establish the pathophysiology of and treatments for these fragility events and to determine their predictive value for HCA.