Diagnostic methods. Microscopic examination of hair
Twisted hair or pili torti is a rare disorder in which the shaft of the hair is flattened and twisted around itself. This disorder has been described in humans. It has a hereditary basis and may be accompanied by other cutaneous and systemic symptoms. In veterinary medicine it has been described in young cats and in bull terriers with acrodermatitis. In cases described in cats, onset usually occurs very early (10 days of age). It may occur alone or in conjunction with other symptoms, such as podal, periocular, or paronychial dermatitis.
Figure 7. Shaft showing longitudinal fragmentation or trichoptilosis.
predisposes the animal to trichoptilosis in response to even mild external trauma, such as the use of topical insecticides. Breakage of the hair in these cases does not usually occur at the base of the shaft, but near the top, resulting in an appearance that is closer to hypotrichosis than alopecia. Trichorrhexis nodosa is the appearance of small deformities in the form of nodules in the hair shaft. These deformities lack cuticle. Breakage of the hair at these nodules gives the hair shaft the appearance of two brooms pushed end to end (Fig. 8). This anomaly has been described in cats continuously treated with topical treatments for flea control.
Figure 8. Trichorrhexis nodosa.
Abyssinian cats can present a hereditary or congenital malformation that affects the tip of the hair and manifests as an onion-shaped swelling. In the case of dogs with diluted coats, melanin forms dispersed clumps of varying sizes in the cortex of the hair but does not result in breakage of the shaft (Fig. 9). If animals with diluted coats develop alopecia, these clumps can group together, creating weak points and secondary breakage of the hair shaft. Follicular casts are sheaths of keratin that cover the hair shaft (Fig. 10) and appear in both primary and secondary keratinisation disorders, such as those associated with sebaceous adenitis, demodicosis, endocrinopathies, primary seborrhoea, and follicular dysplasias.
Figure 9. Accumulation of melanin in the hair shaft cortex
in a dog with a diluted coat.
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