35 Familial canine dermatomyositis
Familial canine dermatomyositis is an inflammatory disease affecting the skin, musculature and blood vessels. It is thought that compromised blood supply causing a low-grade cutaneous ischaemia leads to alopecia, erosions and at times ulceration of the skin. This report describes a case of dermatomyositis in a collie complicated by secondary pyoderma.
Typically, in cases of familial canine dermatomyositis, skin lesions first become apparent between 6 weeks and 6 months of age. The symptoms of myositis generally develop after the onset of skin lesions.
The history in this case was as follows:
Lesions associated with dermatomyositis usually present as alopecia, erythema, scaling, ulceration and crusting. As with many vascular diseases, the extremities and prominences such as the face, tail, pinnae and limbs are mainly affected, so oral, footpad and nail lesions may all be present. Ulceration may develop in more severely affected cases that may also be hyper- or hypopigmented. In general, this is a non-pruritic disease unless there is secondary pyoderma. Temporal muscle atrophy is the most common initial symptom of myositis. Other signs of myositis include dysphagia, facial palsy, stiff gait and a generalized weakness.
Clinical findings in this case were:
Figure 35.1 Multifocal, well-demarcated alopecia and crusting. Crusted erosion is seen above the left eye.
The list of possible differential diagnoses in this case was extensive. Patchy alopecia is suggestive of a folliculitis. The shiny appearance of the skin can be a feature of ischaemic, scarring dermatoses. There were lesions on the pinnae and over the face that were suggestive of a possible autoimmune aetiology. The differential diagnoses therefore included the following:
The initial requirement was to rule out the involvement of parasitic and infectious causes of folliculitis.