Nonbacterial myositis

Amphiregulin in infectious diseases: Role, mechanism, and potential therapeutic targets

Amphiregulin (AREG) serves as a ligand for the epidermal growth factor receptor (EGFR) and is involved in vital biological functions, including inflammatory responses, tissue regeneration, and immune system function. Upon interaction with the EGFR, AREG initiates a series of signaling cascades necessary for several physiological activities, such as metabolism, cell cycle regulation, and cellular proliferation. Recent findings have provided evidence for the substantial role of AREG in maintaining the equilibrium of homeostasis in damaged tissues and preserving epithelial cell structure in the context of viral infections affecting the lungs. The development of resistance to influenza virus infection depends on the presence of type 1 cytokine responses. Following the eradication of the pathogen, the lungs are subsequently colonized by several cell types that are linked with type 2 immune responses. These cells contribute to the process of repairing and resolving the tissue injury and inflammation caused by infections. Following influenza infection, the activation of AREG promotes the regeneration of bronchial epithelial cells, enhancing the tissue's structural integrity and increasing the survival rate of infected mice. In the same manner, mice afflicted with influenza experience rapid mortality due to a subsequent bacterial infection in the pulmonary region when both bacterial and viral infections manifest concurrently inside the same host. The involvement of AREG in bacterial infections has been demonstrated. The gene AREG experiences increased transcriptional activity inside host cells in response to bacterial infections caused by pathogens such as Escherichia coli and Neisseria gonorrhea. In addition, AREG has been extensively studied as a mitogenic stimulus in epithelial cell layers. Consequently, it is regarded as a prospective contender that might potentially contribute to the observed epithelial cell reactions in helminth infection. Consistent with this finding, mice that lack the AREG gene exhibit a delay in the eradication of the intestinal parasite Trichuris muris. The observed delay is associated with a reduction in the proliferation rate of colonic epithelial cells compared to the infected animals in the control group. The aforementioned findings indicate that AREG plays a pivotal role in facilitating the activation of defensive mechanisms inside the epithelial cells of the intestinal tissue. The precise cellular sources of AREG in this specific context have not yet been determined. However, it is evident that the increased proliferation of the epithelial cell layer in infected mice is reliant on CD4+ T cells. The significance of this finding lies in its demonstration of the crucial role played by the interaction between immunological and epithelial cells in regulating the AREG-EGFR pathway. Additional research is necessary to delve into the cellular origins and signaling mechanisms that govern the synthesis of AREG and its tissue-protective properties, independent of infection.

COVID-19-Triggered Acute Liver Failure and Rhabdomyolysis: A Case Report and Review of the Literature

COVID-19 is primarily known for its respiratory tract involvement, often leading to severe pneumonia and exacerbation of underlying diseases. However, emerging evidence suggests that COVID-19 can result in multiorgan failure, affecting organs beyond the respiratory system. We present the case of a 62-year-old male with COVID-19 who developed acute liver failure (ALF) and rhabdomyolysis in the absence of respiratory failure. Initially, the patient presented with significantly elevated aspartate transaminase (5398 U/L) and alanine transaminase (2197 U/L) levels. Furthermore, a prolonged prothrombin time international normalized ratio (INR) of 2.33 indicated the diagnosis of ALF without hepatic coma, according to Japanese diagnostic criteria. The patient also exhibited elevated creatine kinase (9498 U/L) and a mild increase in creatinine (1.25 mg/dL) levels, but both values improved with intravenous fluid support and molnupiravir administration. To our knowledge, this is the first reported case presenting with both ALF and rhabdomyolysis associated with COVID-19. In addition, we review the existing literature to summarize previously reported cases of ALF triggered by SARS-CoV-2. This case report underscores the significance of recognizing COVID-19 as a significant contributing factor in the development of multiorgan failure. Furthermore, it suggests that COVID-19 can lead to severe illness, irrespective of the absence of respiratory failure.

Impaired muscle stem cell function and abnormal myogenesis in acquired myopathies

Skeletal muscle possesses a high plasticity and a remarkable regenerative capacity that relies mainly on muscle stem cells (MuSCs). Molecular and cellular components of the MuSC niche, such as immune cells, play key roles to coordinate MuSC function and to orchestrate muscle regeneration. An abnormal infiltration of immune cells and/or imbalance of pro- and anti-inflammatory cytokines could lead to MuSC dysfunctions that could have long lasting effects on muscle function. Different genetic variants were shown to cause muscular dystrophies that intrinsically compromise MuSC function and/or disturb their microenvironment leading to impaired muscle regeneration that contributes to disease progression. Alternatively, many acquired myopathies caused by comorbidities (e.g., cardiopulmonary or kidney diseases), chronic inflammation/infection, or side effects of different drugs can also perturb MuSC function and their microenvironment. The goal of this review is to comprehensively summarize the current knowledge on acquired myopathies and their impact on MuSC function. We further describe potential therapeutic strategies to restore MuSC regenerative capacity.

[A case of anti-SRP antibody-positive immune-mediated necrotizing myopathy triggered by human parvovirus B19 infection]

We have reported a case of a 44-year-old woman with anti-signal recognition particle (SRP) antibody-positive immune-mediated necrotizing myopathy triggered by human parvovirus B19 (PVB19) infection. She was admitted to the hospital because of lower leg edema and muscle weakness after erythema infectiosum. Magnetic resonance imaging of the lower extremities revealed high signals in the proximal muscles and subcutaneous edema on STIR. Muscle biopsy showed myofiber regenerative changes and variation in fiber size. A myositis-specific autoantibody profile indicated a positive result for anti-SRP antibodies. We diagnosed the patient with immune-mediated necrotizing myopathy (IMNM). Muscle strength and subcutaneous edema improved gradually in 3 months following immunotherapy. This is the first case report of an IMNM associated with PVB19 infection.

Value of strain-wave sonoelastography as an imaging modality in assessment of benign acute myositis in children

Background/aim

Although sonoelastography is applied in assessment of many organs, studies for evaluation of muscles are very few in number and are mostly limited to adults. With this prospective study, we aimed to evaluate the value of sonoelastography in assessment of influenza related benign acute myositis in children.

Materials and methods

This study enrolled 25 patients with a clinical diagnosis of benign acute childhood myositis (BACM) and 25 age and sex-matched healthy controls. All patients presented to our emergency department with the complaint of inability to walk and had increased serum creatine kinase (CK) levels. All patients underwent strain elastography of the gastrocnemius muscle, and an elastography score was assigned to each patient by using a previously published 5 point-color scoring system. The findings were compared with those of the control group.

Results

No statistically significant difference was detected regarding age, weight, height, or body mass index (BMI) between patient and control groups. A statistically significant difference was found between the final elastography scores of the patient and control groups, mean values being 4.16 ± 0.75 versus 3.08 ±0.40, respectively (p < 0.001). Sonoelastography yielded a sensitivity of 80%, positive predictive value of 87%, specificity 88%, negative predictive value of 81.5%, and an overall accuracy of 84 %.

Conclusion

Sonoelastography proves to be a valuable tool for diagnosis of BACM. It is one of the available ultrasound techniques in a radiology department and may particularly evolve to become a useful routine ancillary technique for investigation and follow-up in these cases.

A crawling case of benign acute childhood myositis

Benign acute childhood myositis is a relatively uncommon complication of viral illness, particularly influenza A and B infections. In this abstract, we present a case report of benign acute childhood myositis secondary to influenza. On presentation, he was ill-appearing, febrile and had significant calf pain that limited mobility. Examination revealed mildly erythematous throat and bilateral calf tenderness with pain on dorsiflexion bilaterally. A respiratory virus panel was positive for influenza A subtype H3 and he was found to have an elevated creatine phosphokinase. He was diagnosed with benign acute childhood myositis secondary to influenza type A infection and symptoms gradually resolved following supportive management. Management involves oral hydration, pain management, and follow-up to ensure resolution. Extensive laboratory evaluation and hospitalization are often unnecessary. Benign acute childhood myositis is self-limiting with an excellent prognosis and should be included in the differential for a child who develops difficulty walking, particularly when presentation follows a respiratory infection.

Trismus originating from rare fungal myositis in pterygoid muscles: A case report

BACKGROUND

Trismus is a common problem with various causes. Any abnormal conditions of relevant anatomic structures that disturb the free movement of the jaw might provoke trismus. Trismus has a detrimental effect on the quality of life. The outcome of this abnormality is critically dependent on timely diagnosis and treatment, and it is difficult to identify the true origin in some cases. We present a rare case of trismus due to fungal myositis in the pterygoid muscle, excluding any other possible pathogenesis.

CASE SUMMARY

The patient presented with a 2-mo history of restricted mouth opening. Computed tomography showed obvious enlargement of the left pterygoid muscles. Furthermore, the patient had trismus without obvious predisposing causes. The primary diagnosis was pterygoid myosarcoma. Consequently, lesionectomy of the left pterygoid muscle was performed. Intraoperative frozen biopsy implied the possibility of an uncommon infection. Postoperative pathologic examination confirmed myositis and necrosis in the pterygoid muscle. Fungi were detected in both muscle tissue and surrounding necrotic tissue. The patient recovered well with antifungal therapy and mouth opening exercises. The rarity of fungal myositis may be responsible for the misdiagnosis. Although the origin of pathogenic fungi is still unknown, we believe that both hematogenous spread and local invasion could be the most likely sources. To the best of our knowledge, this is the first case in the literature that reported fungal myositis in pterygoid muscles as the only reason that results in trismus.

CONCLUSION

Surgeons should remain vigilant to the possibility of trismus originating from fungal myositis.

A brief review of influenza virus infection

Influenza is an acute viral respiratory infection that affects all age groups and is associated with high mortality during pandemics, epidemics, and sporadic outbreaks. Nearly 10% of the world's population is affected by influenza annually, with about half a million deaths each year. Influenza vaccination is the most effective method for preventing influenza infection and its complications. The influenza vaccine's efficacy varies each season based on the circulating influenza strains and vaccine uptake rates. Currently, three antiviral drugs targeting the influenza virus surface glycoprotein neuraminidase are available for treatment and prophylaxis of disease. Given the significant burden of influenza infection globally, this review is focused on the latest findings in the etiology, epidemiology, transmission, clinical manifestation, diagnosis, prevention, and treatment of influenza.

Analysis of human total antibody repertoires in TIF1γ autoantibody positive dermatomyositis

We investigate the accumulated microbial and autoantigen antibody repertoire in adult-onset dermatomyositis patients sero-positive for TIF1γ (TRIM33) autoantibodies. We use an untargeted high-throughput approach which combines immunoglobulin disease-specific epitope-enrichment and identification of microbial and human antigens. We observe antibodies recognizing a wider repertoire of microbial antigens in dermatomyositis. Antibodies recognizing viruses and Poxviridae family species are significantly enriched. The identified autoantibodies recognise a large portion of the human proteome, including interferon regulated proteins; these proteins cluster in specific biological processes. In addition to TRIM33, we identify autoantibodies against eleven further TRIM proteins, including TRIM21. Some of these TRIM proteins share epitope homology with specific viral species including poxviruses. Our data suggest antibody accumulation in dermatomyositis against an expanded diversity of microbial and human proteins and evidence of non-random targeting of specific signalling pathways. Our findings indicate that molecular mimicry and epitope spreading events may play a role in dermatomyositis pathogenesis.

Megremis, Walker at al. identify immunogenic epitopes in dermatomyositis patients. They identify antibodies recognizing a wider diversity of microbial antigens including poxviruses, and autoantibodies recognizing a large portion of the human proteome. Shared epitope homology between viral and human proteins suggests that molecular mimicry and epitope spreading events may play a role in dermatomyositis pathogenesis.

Secondary Causes of Myositis

Purpose of review

The purpose of this paper is to comprehensively evaluate secondary causes of inflammatory myopathies (myositis) and to review treatment options.

Recent findings

This review highlights recent advancements in our understanding of known causes of myositis, including newer drugs that may cause myositis such as checkpoint inhibitors and viruses such as influenza, HIV, and SARS-CoV2. We also discuss treatment for malignancy-associated myositis and overlap myositis, thought to be a separate entity from other rheumatologic diseases.

Summary

Infections, drugs, rheumatologic diseases, and malignancies are important causes of myositis and are important to diagnose as they may have specific therapies beyond immunomodulatory therapy.

Rare case of extensive streptococcal myositis

A rare case of extensive streptococcal myositis is reported. A 46-year-old man was admitted following acute swollen right elbow joint associated with localised pain, erythema and hypoaesthesia. Multiple tense blisters subsequently developed around the affected elbow joint extending to the axilla. He was treated for suspected soft tissue infection and septic arthritis. Blood test investigations demonstrated raised creatine kinase (894 U/L) and inflammatory markers (white cell count 21.1×10⁹/L; C reactive protein 370 mg/L). Emergency CT scan reported extensive myositis affecting the triceps, latissimus dorsi and pectoralis major muscle with no fascial involvement. He was escalated to intensive care unit and treated for infectious myositis. Further investigation revealed positive streptococcal antibody (anti-streptodornase B titre >1600 U/mL). He was managed conservatively with microbiologist specialist input and supportive care. The patient made good recovery after receiving 10 days of intravenous antibiotics and subsequently switched to oral antibiotics. He was discharged on day 30 of admission after receiving intensive inpatient physiotherapy.

COVID-Activated Emergency Scaling of Anesthesiology Responsibilities Intensive Care Unit

In response to the rapidly evolving coronavirus disease 2019 (COVID-19) pandemic and the potential need for physicians to provide critical care services, the American Society of Anesthesiologists (ASA) has collaborated with the Society of Critical Care Anesthesiologists (SOCCA), the Society of Critical Care Medicine (SCCM), and the Anesthesia Patient Safety Foundation (APSF) to develop the COVID-Activated Emergency Scaling of Anesthesiology Responsibilities (CAESAR) Intensive Care Unit (ICU) workgroup. CAESAR-ICU is designed and written for the practicing general anesthesiologist and should serve as a primer to enable an anesthesiologist to provide limited bedside critical care services.

Two case reports of distal upper limb weakness following influenza-like illness: an emerging pattern of para-infectious myositis in adults

Background

Myositis is a recognised complication of numerous systemic viral infections including influenza. In adults the typical pattern is characterised by myalgia and marked proximal muscle weakness in upper and lower limbs and resolves slowly over weeks rather than days.

Case presentation

Here, we describe two male patients with myositis with an unusual distribution of weakness in the distal upper limbs, which both followed a flu-like illness and resolved spontaneously. Both patients had moderate elevations in creatine kinase, extensive negative serological investigations, normal nerve conduction studies and myopathic changes on electromyography.

Conclusions

In the para-infectious context, myositis is an important differential of acute distal upper limb weakness. This unusual pattern of acute muscle weakness should be recognised to avoid unnecessary in treatments. Similar cases in the recent literature in male patients between the ages of 25 to 55 are reviewed and suggest an emerging pattern of para-infectious myositis.

Chikungunya virus replication in skeletal muscle cells is required for disease development

Chikungunya virus (CHIKV) is an arbovirus capable of causing a severe and often debilitating rheumatic syndrome in humans. CHIKV replicates in a wide variety of cell types in mammals, which has made attributing pathologic outcomes to replication at specific sites difficult. To assess the contribution of CHIKV replication in skeletal muscle cells to pathogenesis, we engineered a CHIKV strain exhibiting restricted replication in these cells via incorporation of target sequences for skeletal muscle cell-specific miR-206. This virus, which we term SKE, displayed diminished replication in skeletal muscle cells in a mouse model of CHIKV disease. Mice infected with SKE developed less severe disease signs, including diminished swelling in the inoculated foot and less necrosis and inflammation in the interosseous muscles. SKE infection was associated with diminished infiltration of T cells into the interosseous muscle as well as decreased production of Il1b, Il6, Ip10, and Tnfa transcripts. Importantly, blockade of the IL-6 receptor led to diminished swelling of a control CHIKV strain capable of replication in skeletal muscle, reducing swelling to levels observed in mice infected with SKE. These data implicate replication in skeletal muscle cells and release of IL-6 as important mediators of CHIKV disease.

[Infectious myositis]

Infectious myositis is a rare condition that can be caused by bacteria, viruses, parasites or fungi. Muscle pain or weakness are symptoms shared by all type of myositis. Diagnosis is made on clinical presentation: fever and poor general state is found in bacterial myositis, diffuse muscle pain with flu-like symptoms in viral causes, eosinophilia and a tropical travel history can be related to parasitic etiology, and immunocompromising condition suggests fungal infection. Rhabdomyolysis, leukocytosis and elevated C-reactive protein are common. Imaging (computed tomography or magnetic resonance imaging) can be useful to detect which muscle is affected. The causative organism can be identified on blood cultures, skeletal muscle biopsy, serology or any other pathogen specific test. Treatment depends on the causative organism. Open surgical or imaging-guided drainage is usually necessary in bacterial myositis.

Discrimination between tuberculous and bacterial pyomyositis in magnetic resonance features

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Discriminating imaging features between bacterial and tuberculous pyomyositis.

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T2 high signal intensity at abscess wall can predict for bacterial pyomyositis.

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Abscess wall character on imaging of bacterial muscle infection.

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Magnetic resonance imaging between bacterial and tuberculous muscle infection.

Purpose

The purpose of this study was to assess the differences of magnetic resonance features between tuberculous and bacterial pyomyositis.

Method

This is a retrospective study of patients with bacterial and tuberculous pyomyositis. We excluded patients with pyomyositis caused by actinomycosis, non-tuberculous mycobacterium, fungi, unknown of causative organism, or inadequate imaging for analysis. Magnetic resonance imaging was independently reviewed by two radiologists.

Results

Of the 136 pyomyositis patients, 71 (52.2 %) patients had bacterial pyomyositis while 65 (47.8 %) patients had tuberculous pyomyositis. Seventy-seven patients (56.6 %) had intramuscular abscess. On multivariable analysis, bacterial pyomyositis was associated with diabetes mellitus (odds ratio [OR] 3.17, 95 % confidence interval [CI] 1.30–8.24) and bone marrow involvement (OR 5.02, 95 % CI 1.21–34.4). Spinal involvement had a significantly lower likelihood of bacterial pyomyositis (OR 0.25, 95 %CI 0.11–0.54). In patients with intramuscular abscess, diabetes mellitus and hyperintense on T2-weighted images at the abscess wall had a significantly higher likelihood of bacterial pyomyositis (OR 5.21, 95 %CI 1.33–25.42 and OR 5.34, 95 %CI 1.36–24.71, respectively), whereas spinal involvement had a significantly lower likelihood of bacterial pyomyositis (OR 0.09, 95 %CI 0.02–0.30).

Conclusions

Magnetic resonance imaging has modest accuracy for differentiation of tuberculous and bacterial pyomyositis. Diabetes mellitus and extraspinal pyomyositis were the predictors of bacterial pyomyositis. Presence of T2 hyperintense wall of intramuscular abscess was also the predictor of bacterial pyomyositis.

Severe rhabdomyolysis associated with severe fever with thrombocytopenia syndrome in a married couple: a case report

Background

Severe fever with thrombocytopenia syndrome (SFTS) is a tick-borne infection that has recently emerged. This infectious disease is due to the transfer of SFTS virus (SFTSV) from the infected blood of animals to humans. Approximately 30% of patients who are infected with SFTS die from multiorgan failure associated with severe infection, systemic inflammatory response syndrome, or disseminated intravascular coagulation. We treated an elderly Japanese couple (husband and wife) who had genetically identical SFTSV infections and who both developed severe rhabdomyolysis.

Case presentation

An 80-year-old man presented to the clinic with a fever; his 74-year-old wife presented with a fever 9 days later. Their laboratory results at diagnosis showed severe rhabdomyolysis with significantly elevated creatinine kinase (detected levels: husband, 9546 U/L; wife, 15,933 U/L). The creatinine kinase isozyme was 100% MM type in both patients. In both the husband and wife, SFTSV was identified with real-time polymerase chain reaction analysis. The detected SFTSVs in both the husband and wife were identical according to the genome sequence analysis. The husband’s bone marrow indicated macrophage activation syndrome, but he responded to supportive therapy. He was discharged after being hospitalized for 32 days. The wife was admitted to our hospital in critical condition 2 days after SFTS symptom onset. She died of multiorgan failure 8 days after onset, despite being cared for in an intensive care unit. Both of the patients presented with rhabdomyolysis following SFTS symptom onset. The patients’ clinical outcomes were different from each other; i.e., the husband survived, and the wife died.

Conclusions

SFTSV infection-associated rhabdomyolysis has been reported in one patient, and simultaneous onset in two related patients has not been described previously. Our findings suggest that similar biological responses occurred, but they resulted in different clinical outcomes in the patients infected by the identical SFTSV isolates. Notably, a patient’s clinical outcome depends on their own immune response. We suggest that one component of viral rhabdomyolysis involves immune-mediated responses. Severe immunological responses may adversely affect the treatment outcome, as demonstrated by the wife’s clinical course. Our findings demonstrate that a patient’s immune response contributes to their prognosis following SFTSV infection.

Therapeutic administration of IL-10 and amphiregulin alleviates chronic skeletal muscle inflammation and damage induced by infection

Maintenance of tissue integrity in skeletal muscle requires the immunomodulatory and regenerative functions of muscle-resident regulatory T cells (Tregs). Chronic skeletal muscle infections, such as with Toxoplasma gondii disrupt normal immuno-regulatory networks and lead to pathogenic changes in Treg function. Specifically, Tregs during chronic T. gondii infection reinforce an inflammatory macrophage bias that exacerbates injury in skeletal muscle. In this study, we investigated whether the aberrations in skeletal muscle Treg function during chronic infection could be overcome by treatment with Treg-related factors associated with enhanced muscle regeneration during sterile injury. We show treatment of chronically infected mice with the Treg promoting therapies, interleukin-2 complexed with anti-IL-2 antibody or interleukin-33 (IL-33), did not restore macrophage dynamics or muscle function, respectively, in vivo. However supplementation of known Treg-derived factors, interleukin-10 (IL-10) and amphiregulin (Areg) improved muscle function and skewed macrophages toward a restorative phenotype in the presence of chronic infection. These shifts in macrophage phenotype are coupled with enhanced physiologic parameters of regeneration. Together, these data suggest that while Treg-mediated immuno-regulation is compromised during chronic skeletal muscle infection, supplementation of canonical Treg-derived factors such as IL-10 and Areg can restore immunologic balance and enhance muscle repair.

Focal myositis: A review

Amongst the heterogeneous group of inflammatory myopathies, focal myositis stands as a rare and benign dysimmune disease. Although it can be associated with root and/or nerve lesions, traumatic muscle lesions and autoimmune diseases, its triggering factors remain poorly understood. Defined as an isolated inflammatory pseudotumour usually restricted to one skeletal muscle, clinical presentation of focal myositis is that of a rapidly growing solitary mass within a single muscle, usually in the lower limbs. Electromyography shows spontaneous activity associated with a myopathic pattern. MRI reveals a contrast enhanced enlarged muscle appearing hyper-intense on FAT-SAT T2 weighted images. Adjacent structures are spared and there are no calcifications. Serum creatine kinase (CK) levels are usually moderately augmented and biological markers of systemic inflammation are absent in most cases. Pathological histological features include marked variation in fibre size, inflammatory infiltrates mostly composed of T CD4+ lymphocytes and macrophages, degenerating/regenerating fibres and interstitial fibrosis. Differential diagnoses are numerous and include myositis of other origin with focal onset. Steroid treatment should be reserved for patients who present with major pain, nerve lesions, associated autoimmune disease, or elevated C reactive protein or CK.

More parasitic myositis cases in humans in Australia, and the definition of genetic markers for the causative agents as a basis for molecular diagnosis

Since 1998, there have been six reported human cases of myositis in Australia, attributable to infection with the nematode Haycocknema perplexum. However, an unequivocal diagnosis of H. perplexum infection and associated disease has been seriously compromised by a lack of molecular markers for this nematode. Here, we report new cases of disseminated myositis in two male patients from the states of Queensland and Tasmania in Australia, respectively; genetically characterize the causative agent from each case; and, also establish a PCR-based sequencing approach as a tool to support the diagnosis of future cases and to underpin epidemiological studies.

Neuromyelitis optica preceded by hyperCKemia and a possible association with coxsackie virus group A10 infection

We report the case of a 48-year-old woman presenting with an elevated serum creatine kinase level (hyperCKemia) associated with an initial attack of neuromyelitis optica (NMO). The patient initially showed general fatigue with fever. Laboratory findings showed hyperCKemia and subsequently she developed a slight weakness of both lower limbs and reduced vision. Autoantibodies against aquaporin 4 were found in her serum, and a retrospective examination of viral titers indicated a possible coxsackie virus group A10 infection. The present case suggests that hyperCKemia-mediated disease onset is involved in some patients with NMO, and furthermore, it may be related to muscular destruction associated with viral infection.

Parasitic infections and myositis

Infectious myositis may be caused by a wide variety of bacterial, fungal, viral, and parasitic agents. Parasitic myositis is most commonly a result of trichinosis, cystericercosis, or toxoplasmosis, but other parasites may be involved. A parasitic cause of myositis is suggested by history of residence or travel to endemic area and presence of eosinophilia. The diagnosis of parasitic myositis is suggested by the clinical picture and radiologic imaging, and the etiologic agent is confirmed by parasitologic, serologic, and molecular methods, together with histopathologic examination of tissue biopsies. Therapy is based on the clinical presentation and the underlying pathogen. Drug resistance should be put into consideration in different geographic areas, and it can be avoided through the proper use of anti-parasitic drugs.