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NEUROMUSCULAR CASE OF THE MONTH - AUGUST 2002
Myositis and dermatitis in a 10 year old female spayed Miniature Schnauzer
Contributed by Dr. Karen L. Kline
Iowa State University
Ames, IA
Clinical History
Three weeks prior to presentation, the referring
veterinarian described “noisy breathing” and significant phlegm in the back of
the throat that minimally improved 6 days after the first examination. Clavamox
was prescribed. Ten days later, the dog developed scattered, crusty skin lesions
that had a diffuse pattern. At that time the dog had a dramatically elevated creatine
kinase (CK) and the owner complained of progressive weakness. Dexamethsone
(unknown dosage) and concurrent use of Clavamox did not yield any improvement.
Vaccinations were current and the dog had no travel history.
Physical and Neurological Examination
Upon presentation at the Veterinary Teaching Hospital, the
physical examination was within normal limits with the exception of diffuse,
multifocal crusty skin lesions that were non-ulcerative and
non-painful. The neurological examination revealed normal mentation
and a bilateral CN 7 paresis (Fig. 1) with normal CN 5 sensory function. There
were no signs of spinal cord dysfunction and myotatic
reflexes were normal. The dog had marked diffuse temporal and
masseter muscle atrophy and moderately diffuse
appendicular muscle atrophy (Fig. 2). Difficulty prehending and swallowing food
was observed and there was increased salivation. Neurological localization
supported a generalized lower motor neuron dysfunction. A myopathy was
suspected due to the diffuse muscle atrophy and history of CK elevation. |
Figure 1.
Figure 2.
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Diagnostic Testing
CBC – No significant abnormalties
Serum Chemistry including bile acids – Elevated CK (11,847; reference 60-270)
Premium Thyroid Panel (MSU) – Within normal limits
Thoracic Radiographs – Mild right-sided cardiac enlargement
Abdominal Radiographs – Multiple uroliths
Ophthalmic examination – Healing corneal ulcer OD
Fungal culture of skin lesions and skin scrapings – Negative
Electromyography – Under general anesthesia with isofluorane,
fibrillation potentials and positive sharp
waves were found in the triceps, extensor carpi radialis, cranial
tibial, laryngeal, and tongue muscles.
Muscle and Nerve Biopsies
Similar pathological changes were present within the vastus lateralis, cranial tibial and triceps muscle biopsies. There was a moderate variation in
myofiber size with atrophic fibers having a round shape and surrounded by endomysial fibrosis. Most atrophic fibers contained internal nuclei. Multifocal areas
of mononuclear cell infiltration were present having an endomysial and perimysial distribution with invasion of non-necrotic fibers (Fig. 3, H&E). The
cell population was composed predominantly of macrophages (Fig. 4, esterase) with scattered clusters of lymphocytes. No organisms were observed. No abnormalities
were identified within a biopsy from the peroneal nerve. |
Figure 3. (H&E)
Figure 4. (Esterase) |
Skin Biopsy
Biopsies from the haired skin showed ulcerative and
suppurative dermatitis, and cell-poor interface lymphohistiocytic
dermatitis. These changes were suggestive of erythema multiforme (EM),
toxic epidermal necrolysis (TEN), drug reaction, or
generic dog food dermatosis. The dog had received Clavamox and
dexamethasone prior to admission.
Diagnosis and Conclusion
Inflammatory myopathy/polymyositis and cell-poor interface
lymphohistiocytic dermatitis most likely associated with an idiosyncratic
drug hypersensitivity or toxicity. TEN and EM are commonly caused by drugs.
Levamisole, penicillins, cephalosporins, and sulfonamides are commonly
implicated. Several drugs have also been reported to produce an inflammatory
myopathy including penicillamine, cimetidine and trimethoprim-sulfa. Due to
financial constraints and a very low suspicion of disease, antibody titers
against infectious agents were not performed. Prednisone at immunosuppressive
dosages and supportive care including syringe feeding of a liquid diet were
initiated. Unfortunately, the dog was euthanitized due to poor quality of
life 3 weeks after initiation of therapy according to the owner. A necropsy
was not performed.
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