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Alopecia in dogs, a symptom of many pathologies.
Hair loss in dogs, or alopecia, can be attributed to many causes, and it is to be considered as a symptom of an underlying disease.
Focal or diffuse alopecia?
The first major distinction is between focal and multifocal alopecia (inflammatory type) and diffuse and/or bilateral alopecia (non-inflammatory type). Those represent a large group of skin diseases, united by thinning or lack of hair, absence of itching (which differentiates them from scratching alopecia due to allergic causes), and negative results of fungal tests and skin scrapings.[1; 2]
Patchy (or focal) alopecia can be caused by bacterial, fungal or parasitic infections affecting the hair follicle. Among the most common bacterial infections is pyoderma, which leads to the formation of pustules and scabs on the skin. The most common fungal infections are ringworm and dermatophytosis. Finally, the most common parasitic infection is red mange (or demodectic mange).
Diffuse alopecia, what does it mean?
When we talk about diffuse alopecia we have to distinguish 3 broad groups namely:
- Congenital and hereditary forms
- typical of certain naked breeds such as the Mexican hairless
- Forms due to systemic disease, the main ones are
- Cushing's disease, in which an excess of cortisol causes severe telogenisation (atrophy) of all hair follicles;
- hypothyroidism, characterized by a strong slowdown in the hair cycle, with accentuation of alopecia on the most traumatized areas (back of the nose and tail);
- Feminization syndrome caused by testicular tumors. The dog presents a hypotrichosis of the trunk, sometimes associated with hyperpigmentation, oily seborrhea, pendulous foreskin and gynecomastia.
- hair follicle defects including
- colour dilution alopecia (CDA) a lack of hair that affects blue and blond mutants of many breeds, Affected dogs have a normal coat when they are puppies but around one year of age they show progressive alopecia with the presence of scales, blackheads, secondary bacterial infections that can induce itching.
- Recurrent (seasonal) alopecia of the flanks is a form of alopecia of seasonal character that affects the flanks and sometimes the back of dogs mostly of Boxer, English Bulldog, schnauzer and terrier breeds. The skin of the alopecic area is often hyperpigmented. There is progressive shedding during the autumn/winter period with subsequent regrowth in the spring/summer period.
- Pattern baldness alopecia develops progressively behind the ears, ventrally on the chest, abdomen, perineal and caudal regions of the thighs. Alopecia can begin as early as 6 months of age and affects females more frequently. The breeds in which it has been described are Dachshund, Boston terrier, Chihuahua, Whippet, Greyhound and Italian Greyhound.
- Alopecia X Dogs lose hair on the trunk and around the neck, the remaining hair taking on a downy, dry and matted appearance.
Diagnosis and anamnesis
The breed predisposition to some forms of alopecia can help in the differential diagnosis. E.g. Pomeranian Fox and Chow Chow are predisposed to alopecia X, Doberman and Yorkshire terrier are predisposed to colour dilution alopecia.
The age of the patient, besides helping us to distinguish congenital from acquired alopecia, can direct us towards some diseases more frequent in adulthood or old age.
In general, a slow progression is typical of systemic diseases, endocrinopathies, metabolic or nutritional imbalances. A rapid onset e.g. after physiological phenomena (childbirth and breastfeeding), or after severe systemic pathologies (shock or surgery) suggests telogen outflow. Rapid onset alopecia (anagenic outflow) may occur as a consequence of the administration of cytotoxic agents such as methotrexate and cyclophosphamide.
Is there a cure?
- Fungal, bacterial or parasitic forms will require treatment, either local or systemic with antifungals or antibacterials and antiparasitics.
- Hormonal forms require therapy consistent with the disease.
- For congenital and hereditary forms there is no therapy.