Coming off of a long, dark winter as we are in the Midwest, we're confronted with a unique disease seen in certain breeds of dogs. Light responsive alopecia or seasonal flank alopecia is most often seen at this time of the year. It is not well understood but is thought to be from lack of sunlight exposure to the pineal gland. The pineal gland is located at the base of the brain and is the gland responsible for telling bears to hibernate and perhaps telling us to crawl into bed early during these long winters, eat fatty foods, and in general, not have much energy.
DVM, Dipl. ACVD
These changes are not recognized in dogs but physical changes such as truncal alopecia and hyperpigmentation are evident. Light responsive alopecia is logically more common in those areas of the country with dark winters such as the Midwest, the Plains states, parts of New England and Canada. Studies of seasonal affective disorder in humans show an incidence of 2 percent in Florida vs. 10 percent in New Hampshire. When seen in other parts of the country or at other times of the year it may be evident that affected dogs are house bound during the daylight hours for a prolonged period of time. For example, the owner leaves before dawn and arrives home after sunset so the dog is exposed to virtually no natural sunlight. It is not known whether the disease is comparable between humans and animals but what is certain is that a photo period plays a role in both.
Clinically, the patient is affected with alopecia in a bilaterally symmetrical pattern usually involving the flanks with progressive involvement over the dorsal lumbar area. The hair loss is nonpruritic and may be accompanied by hyperpigmentation and follicular keratosis. The typical clinical picture involves the bilateral flanks but other areas such as the dorsal nasal planum, periocular area, preauricular areas and lateral pinna may be involved. There is no sex predilection and the disease may be hereditary as in our practice we had a mother and daughter Boxer affected. Breeds affected include the Boxer, English Bulldog, French Bulldog, Airedale, Doberman Pinscher, Bouvier de Flanders, Scottish Terrier, Shar Pei, Labrador Retriever, Giant Schnauzer and Akita. Differential diagnoses include hypothyroidism, Cushing's disease and alopecia X.
The diagnosis is made by noting the breed affected, areas of the body affected, time of the year the patient is affected, and by performing skin biopsies. Skin biopsies may include follicular atrophy, "foot-like" comedones with excess keratin plugging of the follicular infundibula, normal epidermal thickness, and hyperpigmentation of the basal cell layer.
Examples of truncal alopecia and hyperpigmentation in various breeds with seasonal flank alopecia.
Treatment includes more sunlight exposure and/or melatonin beginning Sept. 23 through March 23 (vernal equinox). The prognosis is good with most patients regrowing hair upon more sun exposure, however some patients skip a year before they regrow hair and some may not regrow hair completely or at all. This appears to be a benign disease but the more common diseases resulting in bilaterally symmetrical alopecia such as Cushing's disease and hypothyroidism should be ruled out.
It is uncertain how the lack of sunlight to the pineal gland results in alopecia of certain specific areas of the body. The role of melatonin release by this gland upon lack of sunlight exposure via the eyes results in depression and lethargy in humans. Prolactin may also play a role as its concentration in the body may be affected by photo period changes and Serotonin concentrations in humans are reduced in dark, cold environments. Oral doses of Melatonin at a range of 3-24mg/day may be helpful in light responsive alopecia. In Canada melatonin injections have been administered on mink farms to cause production of thick coats nonseasonally for the fur industry. It is possible that melatonin injections are more effective than oral melatonin tablets however melatonin injections can be painful. Melatonin has many actions ranging from contraception to use as an antianxiety agent. Its action in seasonal flank alopecia still remains controversial.