A number of other terms for this condition include adult-onset growth hormone deficiency, growth hormone-responsive alopecia, castration-responsive alopecia and adrenal hyperplasia-like syndrome. No significant changes in sex hormone concentrations have been noted in these dogs. Use of estrogen-receptor antagonists have been shown to be ineffective in female dogs, suggesting reproductive hormones may not be involved in the etiology of this condition. However, some dogs have shown elevation in progesterone levels when injected with synthetic ACTH, suggesting a role of pituitary disease in this phenomenon or underlying borderline hyperadrenocorticism.
Alopecia X affects dogs of both sexes regardless of neuter status. The hair loss can first occur at any age and affected dogs present with gradual loss of hair over the trunk and caudal thighs, sparing the head and front limbs. Sometimes the guard hairs are lost first leaving a soft 'puppy' coat. The skin may become intensely hyperpigmented. There are no systemic signs associated with this condition.
Histological examination usually reveals hyperkeratosis, follicular keratosis, excessive tricholemmal keratinization (flame follicles), thin epidermis, few small anagen bulbs, epidermal pigmentation and melanin aggregates within follicular keratin. Dogs with alopecia X also have the lowest percentage of anagen follicles and the highest percentage of telogen follicles.
Apart from alopecia, most dogs are generally unaffected by the condition.
- Dr R Hilton
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