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Therapeutic Management of Masticatory Muscle Myositis in a Dog.

Abstract

A Dalmatian cross dog was presented with history of trismus i.e. difficulty in opening the jaws and bilateral atrophy of masticatory muscles. The dog responded to treatment with Inj. Prednisolone acetate and was successfully managed.

Keywords: Autoimmune; canine myopathy; masticatory muscle myositis; trismus.

Introduction

Masticatory muscle myositis is an autoimmune canine myopathy causing focal inflammation of muscles of mastication including the temporalis, masseter, pterygoid and rostral digastricus, all of which are innervated by mandibular branch of trigeminal nerve (Bolfa et al., 2011; Melmed et al., 2004; Reiter and Schwarz, 2007). There are two phases, the acute phase characterised by jaw pain, trismus and swelling of masticatory muscles and chronic phase, characterised by muscle atrophy (Anderson and Harvey, 1993; Melmed et al., 2004; Pitcher and Hahn, 2007). Therapy involves immunosuppression with corticosteroids till resolution of symptoms and gradual tapering over a period of three to six months. Masticatory muscle myositis is a targeted autoimmune process against type 2 M fibres which are unique to muscles of mastication (Melmed et al., 2004 and Shelton et al., 1985). The classical presentation of masticatory muscle myositis is inability to open the jaws (trismus), jaw pain and swelling or atrophy of masticatory muscles (Evans et al., 2004 and Melmed et al., 2004).

The average age of onset is three years. This disease can occur in any breed including GSD, Labrador Retriever and Golden Retriever etc. Cavalier King Charles Spaniel appears to have a genetic predisposition (Pitcher and Hahn, 2007).

Patients should be examined for evidence of trauma that could have resulted in mandibular fracture or temporo-mandibular joint luxation. Thorough oral examination should be performed under general anaesthesia.

Materials and Methods

A 2 years old male Dalmatian cross dog was presented with history of trismus i.e. difficulty in opening the mouth, difficulty in prehension and bilateral atrophy of masticatory muscles. The dog was examined under general anaesthesia and diagnosed as masticatory muscle myositis as there was no history of trauma and temporo-mandibular joint appeared to be normal. Treatment was instituted with Injection Prednisolone acetate @ 0.5 mg/kg b. wt. I/M, BID for 12 days after which the dog showed improvement in condition and was able to eat. The dog was then put on oral Prednisolone @ 0.5 mg/kg b. wt. for one week and the dose was tapered slowly over a period of 3 months.

Results

The dog responded to immunosuppressive treatment with corticosteroids i.e. Inj. Prednisolone acetate @ 0.5 mg/kg b. wt. BID for 12 days after which the dog showed improvement in condition and was able to eat, then the dog was put on oral Prednisolone @ 0.5 mg/kg b. wt. for one week and then dose was then tapered slowly over a period of 3 months after which treatment was stopped and the case was followed up for a period of two years during which there was no relapse. Though the jaw movement was not completely normal,it was sufficient for dog to eat and lead a normal life.

Discussion

The condition was diagnosed as masticatory muscle myositis, based on the classical symptoms of trismus i.e. difficulty in opening the jaws and bilateral atrophy of muscles of mastication and its response to immunosuppressive treatment with corticosteroids, which is in agreement with earlier findings. The other methods for diagnosis include muscle biopsy, testing for antibody titre against type 2 M fibres, immunohistochemistry, CT, MRI etc. (Caudro et al., 2013; Reiter and Schwarz, 2007; Shelton et al., 1985). The present case responded well to treatment though it was presented in chronic phase of disease as evidenced by bilateral masticatory muscle atrophy but did not return to complete normal state probably because of fibrosis of myofibres. Other modes of immunosuppressive treatment if there is no response to corticosteroids which include Azathioprine, Cyclosporine which are also immunosuppressants have been suggested (Melmed et al., 2004). But the present case responded well to the treatment with Inj. Prednisolone acetate @ 0.5 mg/kg b. wt. BID without any side effects.

Conclusion

The present study puts on record a rare case of masticatory muscle myositis in a 2 year old male Dalmatian cross dog and its treatment. Masticatory muscle myositis needs to be included in differential diagnosis of disorders in dogs with trismus and swelling or atrophy of muscles of mastication and prompt and aggressive immunosuppressive treatment with corticosteroids should be instituted for resolution of the symptoms.

References

Anderson, J.G. and Harvey, C.E. (1993). Masticatory muscle myositis. J. Vet. Dent. 10: 6-8.

Bolfa, P., Muresan, C., Gal, A., Talescu, M., CucC., Borza, G., Nagy, A., Tabaran, Nadas, G. and Catoi, C. (2011). Masticatory myositis of a dog - Case Study. Vet. Med. 68.

Caudro,A., Paolo, F., Asperio, R.M., Rossini, V., Dondi, M., Simonetto, L.A., Cantile, C. and Lorenzo, V. (2013). Use of MRI for the early diagnosis of masticatory muscle myositis. J. Am. Anim. Hosp. Assoc. 49: 347-52.

Evans, J., Levesque, D. and Shelton, G.D. (2004). Canine inflammatory myopathies: a clinicopathologic review of 200 cases. J. Vet. Intern. Med. 18: 679-91.

Melmed, C., Shelton, G.D., Bergman, R. and Barton, C. (2004). Masticatory muscle myositis - Pathogenesis, Diagnosis and Treatment. Compendium. 590-04.

Pitcher, G.D. and Hahn, C.N. (2007). Atypical masticatory muscle myositis in three cavalier King Charles Spaniel littermates. J. Small Anim. Pract. 48: 226-28.

Reiter, A.M. and Schwarz, T. (2007). Computed tomographic appearance of masticatory myositis in dogs:7 cases (1999-2006). J. Am. Vet. Med. Assoc. 231 :924-30.

Shelton, G.D., Cardinet III, G.H., Bandman, E. et al. (1985). Fiber type specific autoantibodies in a dog witheosinophilic myositis. Muscle Nerve. 8:783-90.

Shelton, G.D., Cardinet III, G.H., Bandman, E. et al. (1987). Canine masticatory muscle disorders: A study of 29 cases. Muscle Nerve.10:783-90.

C. Latha (1) and J. Radhakrishna Rao (2)

Veterinary Hospital P.V. Narasimha Rao Telangana Veterinary University Warangal - 506007 (Telangana).

(1.) Assistant Professor and Corresponding author. E-mail: drlatha276@gmail.com

(2.) Assistant Professor
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Title Annotation:Short Communication
Author:Latha, C.; Rao, J. Radhakrishna
Publication:Intas Polivet
Article Type:Clinical report
Date:Jul 1, 2016
Words:999
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