Diagnosing and managing nonpruritic alopeci (Proceedings)
Alopecia in the dog is a common clinical finding. It is most commonly associated with pruritus due to allergic skin disease. There are also many causes of nonpruritic alopecia. Since the skin and hair can only "react" in a limited manner regardless of the triggering event, signalment, history (hx), physical exam (PE) and laboratory testing (eg skin scrapings, skin biopsies, fungal cultures, endocrine testing, intradermal testing, etc) all may be needed to help determine the underlying cause. When performing a skin biopsy in an alopecic disease it is best to submit an elliptical shaped sample that has the tip of one end in the alopecic region and the other tip in the normally haired area. Be sure to request that the sample is sectioned from tip to tip (longitudinally) rather than transversely. This will allow the pathologist to see the progression of the lesion from early to late stages all on one sample.
Once congenital, pruritic or infectious causes of focal to multifocal alopecia have been eliminated, the remaining alopecic diseases are associated with inflammation or interface dermatitis. These can only be differentiated based on microscopic examination of skin biopsies. Vaccine induced alopecia and dermatomyositis are examples of inflammatory alopecic diseases.
Vaccine induced alopecia is most commonly associated with rabies vaccination. The alopecia occurs 2-12 months after administering a rabies vaccine. Small white breeds of dogs seem to be at risk for developing these lesions. SQ or IM injections have no impact on the occurrence of this reaction. Lesions consist of scaling, focal (occasionally multifocal) areas of alopecia, plaques, hyperpigmentation, nodules, erosions, crusts and cutaneous atrophy (scarring). The lesions may also develop at sites distant from the vaccination site. Histologically in addition to typical vasculitis changes, septal panniculitis and focal lymphoid nodules will be seen. Rule-outs are fairly limited but should include demodicosis, dermatophytosis, allergic skin disease and bacterial skin disease.Dermatomyositis occurs as a genodermatosis in collies and shelties or it may occur in adult spontaneously in adults of other breeds. For the inherited form the age of onset is between 6 weeks and 1 year of age- usually before 6 months of age. The lesions may be fairly limited and heal as the puppy matures or they may progress. Usually the lesions stop progressing by the time the dog is a year old. The cutaneous lesions, which are usually the predominant clinical sign, include focal to multifocal areas of alopecia, scaling, crusts, erosions, ulcers, depigmentation, hyperpigmentation and scarring. These lesions occur on the face, mucocutaneous junctions, carpal and tarsal regions and the tip of the tail and ears. Onychodystrophy may also be present. Secondary bacterial pyodermas may occur. Muscle involvement tends to be proportional to the severity of the skin lesions and is usually identified subsequent to the cutaneous lesions developing. These dogs may develop megaesophagus or muscle atrophy involving the muscles of mastication and ambulation. Differential diagnoses for the skin disease include demodicosis, dermatophytosis, superficial bacterial folliculitis, DLE, cutaneous drug reaction, erythema multiformae, vasculitis and epidermolysis bullosa simplex. In the author's experience, puppies are mostly commonly presented with limited facial lesions that the breeder claims are wounds/scars from the other puppies or a cat in the household. Diagnosis is based on signalment, physical examination and histopathologic changes consistent with a vasculopathy.
Treatment for these ischemic skin diseases would include avoiding the trigger (vaccines in the former and remove the dog from the breeding stock in the later) and various immunomodulating drugs. For vaccine-induced alopecia the treatment options include pentoxifylline or surgical excision of the affected area. Pentoxifylline is a methylxanthine derivative that increases RBC deformability and lowers blood viscosity thereby allowing for better blood flow through narrowed/edematous vessels. It also suppresses synthesis of proinflammatory cytokines such as IL-1, IL-4, IL-12 and TNF-α. Pentoxifylline is administered at 15 mg/kg tid. There may be a 30-90 day lag before full clinical response is seen. For dermatomyositis the treatment will depend on the severity of the symptoms. The author treats dermatomyositis with sunlight avoidance, Vitamin E 400-800 IU bid and pentoxifylline. All dogs with dermatomyositis should be neutered. If the dog is moderately affected then tetracycline and niacinamide will be used along with pentoxifylline. Tetracycline and niacinamide (T/N) have various anti-inflammatory & immunomodulating properties. The dosage for tetracycline and niacinamide in dogs or cats <10 kg is 250 mg of each, q 8 hours. For dogs >10kg - 500 mg of tetracycline and 500 mg of niacinamide q 8 hours are administered. If there is a clinical response (may take 2-3 months) the T/N are slowly decreased from tid, to bid to sid. Side effects are rare but include vomiting, anorexia, lethargy, diarrhea and elevated liver enzymes from niacinamide and lower seizure threshold from tetracycline.