Test breedings reveal inheritance mode of SA, DMS
It is difficult to ascertain the genetic mode of transmission of most of these hereditary skin diseases because test breedings are necessary to accurately outline the transmission of the disease.
Two hereditary skin diseases, sebaceous adenitis (SA) and canine familial dermatomyositis (DMS), have had their mode of inheritance uncovered by test breedings. It seems that these formerly uncommon genetic skin diseases are now appearing more often, possibly due to the popularity of the breeds affected by these diseases.
It was initially described in 1987 by Drs. Rosser and Dunstan in the Standard Poodle. It has since been documented in more than 50 breeds, including the Airedale, Maltese, Havanese, St. Bernard, Toy & Miniature Poodle, Bernese Mountain Dog, Irish Setter, Collie, Samoyed, Golden Retriever, German Shepherd, English Springer Spaniel, Viszla, Doberman Pinscher, Basset Hound, Old English Sheepdog, Scottish Terrier, Akita, Miniature Pinscher, Chow Chow, Dachshund, Weimaraner, Lhasa Apso, Dalmatian and mixed breeds. The disease has also been reported in rabbits, cats and humans.
The etiology of the disease is unknown with theories including a possible defect in keratinization which destroys the sebaceous duct and glands, a defect in epidermal or sebaceous lipids, an autoimmune or hypersensitivity reaction, or an infectious cause, although no agents have ever been isolated. Research indicates a hereditary predisposition in the Standard Poodle and possibly the Golden Retriever, Samoyed and Akita. Two test breedings to determine the genetic pattern of SA have been undertaken in the Standard Poodle to yield the results of an autosomal recessive trait.
German Shepherds may experience hair loss over the dorsal lumber area resembling flea allergy dermatitis, although pruritus is usually absent. Akitas may have accompanying systemic signs such as fever, generalized bacterial folliculitis, weight loss, and anorexia. Affected short-haired breeds such as the Viszla, may present with a truncal papular or nodular type eruption that progresses to circular areas of alopecia and scaling that coalesce. In fact, some pathologists believe that two types of SA exist: one affecting short-coated breeds and the other, long-haired dogs. A subclinical state of SA has been reported in the Standard Poodle that may progress to a clinical stage with time.
Unfortunately, the dog could have been bred over several years before showing clinical signs of the disease, producing clinically affected offspring. At this point, the only reliable diagnosis is a skin biopsy obtained from a clinically affected area, preferably the dorsal cervical and lumbar areas. Don't be surprised if a Standard Poodle owner requests that you perform skin biopsies on their dog that appears perfectly normal! It is done to rule out the possible subclinical form of the disease.
Treatment Therapy ranges from topicals such as baby oil, propylene glycol or other emollients to oral natural and/or synthetic Vitamin A, fatty acids and cyclosporine. Antibiotics may be needed for any secondary bacterial pyoderma.
Therapies that have proven not to be helpful include ketoconazole, zinc supplementation, and steroids. When using one of the topicals mentioned above, the patient is bathed in a keratolytic shampoo, rinsed and towel dried. Then the emollient of choice is massaged into the skin and allowed to stay on for 15-30 minutes. The keratolytic shampoo or detergent is then reapplied onto the oiled dog to solubilize the oil and the entire mixture is rinsed off. This is usually repeated at weekly intervals until a successful response is noted, then used as needed.
Oral retinoids such as isotretinoin and etretinate (no longer available) have been used for SA at l-3mg/kg/day. In larger breeds, they can be cost prohibitive. Side effects include elevations in cholesterol/triglycerides and/or dry eye. Cyclosporine at 5mg/kg s-bid has been used successfully in a Miniature Pinscher and Standard Poodle, but again, this may be cost prohibitive in larger breeds.
Canine familial dermatomyositis Canine familial dermatomyositis (DMS) is an inflammatory disease affecting the skin and sometimes muscle, particularly the muscles of mastication.
It has been reported in humans and interestingly, the lesions affect many of the same areas of the body as in our canine patients. DMS should be suspected in young Shetland Sheepdogs, Collies and Welsh Corgis with focal alopecia and/or erythema of the face, carpi, tarsi or tip of the tail. There is thought to be a familial predisposition with the mode of transmission being autosomal dominant. Most patients present with alopecia before 6 months of age.
The diagnosis of DMS is via a skin biopsy placed in 10 percent formalin. Don't forget to send the age, breed and patient's history, including duration of the lesion, time of onset and medications used to treat the patient to aid the pathologist in making an accurate diagnosis. Skin changes present in DMS include vacuolar changes at the dermal-epidermal junction with follicular atrophy and fibrosis. The pathologic skin changes usually result in a scarring alopecia and some patients may never regrow their hair.
Treatment Treatment depends upon the extent of the lesions and includes topical and/or oral steroids, immunosuppressives, pentoxifylline, Vitamin E, and sunlight avoidance.
In the few elderly patients we have seen with DMS, the onset was abrupt and the disease was aggressive, resulting in severe muscle weakening affecting the esophagus and diaphragm. A suspected variant of DMS seen in the Shetland Sheepdog and Collie formerly referred to as idiopathic ulcerative dermatosis, now thought to be cutaneous lupus also affects adult dogs. The lesions usually occur in the axillae and groin and consist of alopecia, erythema, and ulceration resulting from an initial bullous type reaction. This disease may be more difficult to control with the above medications.
As with any genetic disease, there is much about SA and DMS that remains a mystery, particularly their etiology. Thankfully there is usually little difficulty in achieving the diagnosis of these diseases. However, treatment can remain elusive and vary according to each individual patient. It is important to recognize and diagnose these diseases early, so that future breeding and perpetuation of these diseases will be discouraged.