Three Cases of Canine Dermatomyositis-Like Disease

Background: Dermatomyositis is an idiopathic, inflammatory/immunemediated disease of the skin, muscles and blood vessels of hereditary nature and unclear pathogenesis. This familial disease has been described in certain breeds, especially collies and Shetland sheep dogs and is of rare occurrence in mongrel dogs. To describe and discuss three clinical cases of dermatomyositis-like disease and provide a brief review of the literature. Cases: Three young mongrel dogs are included in this report. Case 1: Mandarino, a 4-year-old mongrel dog, having a history of skin lesions for at least a year. Showed an underweight patient, skin ulcers, crusts, alopecia, peri-ocular scarring causing severe lagophthalmia and a corneal ulcer. Muscle atrophy was most notable in the head and legs; the dog had difficulty and pain walking. Treatment was initialised with cephalexin 30 mg/kg BID, pentoxifylline 25 mg/kg BID, and prednisone 2.2 mg/kg SID. The patient was presented after two weeks for follow up; the anaemia and skin condition had improved, the weight had increased by 2 kg, dysphagia and locomotor abnormalities were not present. Case 2: Milagros, a mongrel female dog approximately two years of age, rescued from a shelter. Physical examination showed facial alopecia, erythema and scarring of the periocular skin, crusting and scaling in alopecic areas, pinnae tip necrosis and crusting, ear alopecia, tail tip necrosis and crusting. Also present were distal limb alopecia, crusting and ulcers in areas of trauma in the hock and carpal surfaces; some nails presented onychorhexis and onychoschizia. The patient has been treated for 12 months with a good clinical outcome, with pentoxifylline, azathioprine 2.2 mg/kg EOD alternating with prednisone 1 mg/kg EOD. Case 3: Chuchito, an 11-month-old male mongrel rescued dog had been previously hospitalised due to his skin condition. Physical examination showed depigmented and alopecic areas in the nasal planum, perioral and periocular areas, and inflammation of the palpebral tissues. Necrosis of the distal pinnae, alopecia and scales were evident, along with sloughing of scales and ulcers. Skin lesions were also present in the distal limbs, and alopecia, erythema and some crusting and scales in the carpal, tarsal and digital areas. Onychodystrophy was present in several digits. This study describes the physical examination and the clinical pathological findings, including skin scrapings, fungal cultures, and skin biopsies, in three dogs with dermatomyositis-like disease, as well as the clinical outcomes after slightly different treatment protocols were used. The biopsy results of two dogs showed ischaemic dermatopathy. Discussion: The most common initial signs of the disease are erythema, desquamation and alopecia in the facial area, ears, distal limbs and pinnae in young puppies aged between two and six months of age, followed by pigmentary changes. Muscular lesions are uncommon; when present, they represent the most severe form of this disease. Dysphagia is a common sign and mega-oesophagus may be present. Patients with muscular disease can manifest difficulty walking, with a stiff high gait. The immune mediated pathogenesis of dermatomyositis can relate to triggering factors in some dogs, such as drugs, infections, paraneoplasms, or toxins. Other potential inducing stressors include oestrus, whelping and excessive solar exposure. Dermatomyositis-like or familiar dermatomyositis is diagnosed using clinical findings, histopathology of skin and muscle, and muscle physiology studies. Electromyography, breed predisposition and genetic background can be helpful in some cases. The clinical findings and response to the treatment of all three cases were compatible with dermatomyositis-like disease in mongrel dogs. Keywords: dermatomyositis, dermatopathy, vascular disease, inflammatory myopathies, mongrel dog.