Research Paper Masticatory Muscle Myositis

Research Paper

Masticatory Muscle Myositis Presenting as a Neoplasm in a Young Woman: A Case Report and Review of Literature

Accepted 22rd September, 2016

ABSTRACT

Masticatory muscle myositis is the most common inflammatory myopathy among canines and is associated with an autoimmune process; however, the Hung-Wei Hsu1, Wan-Fu Su2 and Chih- cause is unknown. A 28-year-old young woman was notices with left facial Kung Lin3* swelling and pain, particularly during mouth opening. No obvious trigger factors, including trauma, were found. Computed tomography (CT) scans of the head and 1Department of Pathology, Buddhist Taipei Tzu Chi General Hospital, New neck revealed a heterogenous mass in the left masseter muscle. Due to persistent Taipei City, Taiwan, Republic of China. discomfort, tumor excision was performed. The histopathologic findings of the 2Department of Otolaryngology, mass included several degenerative muscle fibers with enlargement and atrophy Buddhist Taipei Tzu Chi General accompanied by lymphocytic infiltrates. Differential diagnosis including main Hospital, New Taipei City, Taiwan, Republic of China. myopathies was considered, but our case did not fulfill any criteria of these 3Department of Pathology, Buddhist myopathies. Therefore, we diagnosed the patient with masticatory muscle Taipei Tzu Chi General Hospital, New myositis, which is rare in humans. Further investigation is necessary for Taipei City, Taiwan, Republic of China. understanding the disease.

*Corresponding author. E-mail: [email protected]. Tel:(886) 2- Key words: Masticatory muscle myositis, neoplasm, masseter muscle, young 66289779 ex 8926. woman.

INTRODUCTION

Masticatory muscle myositis (MMM) is the most common dental problems, or other systemic disorders. No limb inflammatory myopathy among canines and was weakness, pain, or rash was ever noticed by the patient. extensively investigated. It is restricted to masticatory She initially received conservative treatment including muscles and limb muscles are typically spared. It is also painkillers; however, the symptoms persisted. Laboratory associated with an autoimmune process involving the tests revealed that white blood cell, hemoglobin, platelets formation of auto-antibodies against type 2M muscle fibers and electrolyte counts were within normal limits. in the masticatory muscles, the cause of which is unknown, Computed tomography (CT) (Figure 1) scans of the head although some authors proposed the theory of molecular and neck revealed an irregular heterogeneously enhanced mimicry (Caeley et al., 2004; Tresamol et al., 2012; Quiroz- lesion with a maximum diameter of approximately 3 cm in Rothe et al., 2002; Evans et al., 2004; Jennifer et al., 2003). the left masseter muscle. Clinically, hemorrhage, a In humans, MMM has not been extensively documented degenerative change in muscle and a vascular neoplasm thus far and is rare. Here, we presented a case of MMM in a were first considered and the mass was less likely to be 28-year-old woman and focused on histopathologic malignant due to the location. Sonography-guided findings and differential diagnosis. aspiration cytology of the lesion revealed the presence of only inflammatory cells and finally, tumor excision was performed. Case report The gross tumor consisted of two friable fragments measuring up to 1.0 × 1.0 × 0.5 cm in size, soft to elastic in A 28-year-old woman experienced left facial swelling and consistency and tan in color. Microscopically, the tumor pain, particularly during mouth opening, for was composed of skeletal muscle tissue with degenerative approximately 2 months. She had no history of trauma, and focal atrophic changes characterized by fused and

Academia Journal of Scientific Research; Hsu et al. 305

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Figure 1. Head and neck CT reveals a heterogenous lesion within the left masseter muscle; A) Axial view and (B) sagittal view.

small round muscle fibers. Figure 2 shows the Endomysial IBM. Eosinophilic inclusion bodies can be identified and or perifascicular infiltration with lymphocytes. Masson confirmed using histochemical staining, such as amyloid trichrome staining demonstrated the muscular immunostaining. Muscular dystrophy is less suspected characteristic of the degenerative mass. Both Congo red because of the absence of limb weakness and staining and amyloid immunostaining were negative for predominance in men (Dalakas, 1991, 2011, 2010; Janice amyloid accumulation. The histopathologic findings and et al., 2013; Askanas et al., 2009, 1992). histochemical and immune-histochemical staining were Myositis ossificans can involve the masseter muscles and consistent with MMM rather than a true neoplasm. this condition is often attributed to trauma. Imaging and histopathological studies can be used to identify osseous lesions (Piombino et al., 2013; Muralidhar et al., 2014). RESULTS AND DISCUSSION Idiopathic eosinophilic myositis is a rare disease characterized by hypereosinophilia in peripheral blood We presented a case of unilateral MMM in a young woman and/or in the bone marrow and eosinophilic infiltration of without related factors such as trauma, infection and the skeletal muscle accompanied by parasitic infections or autoimmune disease and no other muscle or organ other systemic disorders (Krahn et al., 2006). involvement was found. Differential diagnoses including a Based on a review of the literature, our case did not group of inflammatory myopathies, myositis ossificans and fulfill any criteria of the aforementioned myopathies due eosinophilic myositis/perimyositis was considered. to the unique location, absence of limb weakness and non- Dermatomyositis (DM) affects children and adults from specific histopathologic findings. Therefore, we diagnosed young to middle age and is predominant in female patients the patient with MMM, which is rare in humans and is and such patients often present preceding skin rashes easily misinterpreted as a neoplasm. We cannot before developing muscle weakness. Microscopically, completely exclude that MMM may be an initial characteristic perifascicular atrophy with mild or absent manifestation of one of the aforementioned myopathies inflammatory cell infiltrates was observed. Polymyositis and we planned to continue follow-up of this patient. (PM) affects adults and is predominant in women which results in symmetrical proximal muscle weakness. No specific microscopic features were observed for PM. Conclusion Inclusion body myositis/myopathy (IBM) often affects adults in the sixth decade of life and is predominant in men MMM is rare and has not been extensively documented in and results in asymmetrical limb muscle weakness. humans and easily misinterpreted as a neoplasm. We Microscopically, typical rimmed vacuoles within muscle presented the case of MMM in a young woman; however, fibers and endomysial infiltrates with mononuclear cells the collection of additional cases and further investigation between normal-appearing muscle fibers are observed in are necessary for understanding of the disease. Academia Journal of Scientific Research; Hsu et al. 306

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Figure 2. Pathological findings of masticatory muscle myositis; (A) At low-power magnification (40×), the dense aggregates of pale to eosinophilic bodies surrounded by normal skeletal muscles are observed. Note the enlarged and preserved architecture of muscle fibers; (B) At high-power magnification (400×), the transitional zone between normal skeletal muscle and degenerative skeletal muscle is observed and (C, D) Infiltration of mononuclear inflammatory cells is present and demonstrated by immune-histochemical staining of the leukocyte common antigen.

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