Alopecia X

Rosario Cerundolo, Six Mile Bottom, Suffolk, United Kingdom

Alopecia X is a form of canine adult-onset alopecia that was formerly known by various names (Box 115-1). However, this diversity in names is merely descriptive and is based on the differences in endocrine findings or clinical responses to various therapeutic modalities. Alopecia X mainly affects Nordic breeds (Samoyed, Siberian husky, spitz, and Alaskan malamute) but may also affect the chow-chow, Pomeranian, and miniature poodle. Alopecia X is probably a clinical spectrum of different conditions. It is not yet proven that Alopecia X in the aforementioned breeds actually is a single disease entity with similar causes and pathogenesis.

Box 115-1 Synonyms of Alopecia X

1. Pseudo–Cushing’s syndrome

2. Growth hormone deficiency of the adult dog

3. Hyposomatotropism of the adult dog

4. Growth hormone–responsive dermatosis

5. Castration-responsive dermatosis

6. Sex hormone dermatosis

7. Estrogen-responsive dermatosis

8. Testosterone-responsive dermatosis

9. Biopsy-responsive alopecia

10. Adrenal sex hormone disorder

11. Congenital adrenal hyperplasia

12. o,p′DDD-responsive dermatosis

13. Nordic breed follicular dysplasia

14. Follicular dysplasia of the Siberian husky and malamute

15. Malamute coat funk

16. Woolly syndrome

17. Black skin disease

18. Hair cycle arrest

o,p′DDD, Mitotane.

Alopecia X usually starts in dogs between 1 and 3 years of age, although cases have been reported in 9-month-old puppies and 11-year-old dogs. Intact males seem to be predisposed.

Pathogenesis

The pathogenesis of alopecia X remains poorly understood. A genetic predisposition to a hormone production defect or abnormal hormone action on the hair follicle is suspected. Arguments in favor of a defect in sex hormone production include hair regrowth in affected dogs following neutering or treatment with products that affect sex hormone production and elevated levels of certain sex hormones, especially 17-hydroxyprogesterone (17-OHP), following adrenocorticotropic hormone (ACTH) stimulation in some affected dogs. It has been proposed that alopecia X in miniature poodles and Pomeranians may be a variant of pituitary-dependent hyperadrenocorticism (Cerundolo et al, 2007).

Clinical Signs

Alopecia X is a disease that exclusively affects the hair coat and skin of dogs. Dogs are normally healthy. If there are signs of systemic disease, other endocrine diseases should be suspected.

Initially there is sparse loss of guard hairs resulting in a dull, dry coat. Sometimes a more generalized loss of guard hairs gives the coat a “puppy” appearance. The hair coat may also appear lighter or a different color with the loss of guard hairs. Hair loss may be noted first in frictional areas such as around the neck, tail head region, and caudal thighs, and these areas become more severely involved with time. The progression from early changes in hair coat to complete hair loss may take several years in some dogs. The retained secondary hairs are also lost with time, which results in complete alopecia of the affected areas. The exposed skin may become hyperpigmented. It is likely that the increased pigmentation is the result of sun exposure and can be minimized with sun restriction or use of clothing. Owners may first become aware of the problem when the dog’s hair coat fails to regrow after clipping. This can also be seen in endocrine diseases or in Nordic or plush-coated breeds that were shaved during the normal telogen phase of the hair cycle. Hair regrowth is often seen in areas of trauma (e.g., skin scraping or biopsy sites). Secondary skin infections are rare in this condition.

Diagnosis

There is no test that can definitively diagnose alopecia X in a dog. The diagnosis is often made by exclusion (Box 115-2). Other endocrine diseases such as hyperadrenocorticism, hypothyroidism, and hyperestrogenism, as well as breed-specific hair cycle abnormalities, color dilution alopecia, black hair follicular dysplasia, telogen effluvium, and anagen effluvium, should be ruled out. Sometimes affected dogs have thyroid test results suggestive of hypothyroidism (low total thyroxine level), but other thyroid test results are normal. In those cases thyroid supplementation fails to cause hair regrowth.

Box 115-2 Criteria Commonly Used by the Author to Confirm a Diagnosis of Alopecia X