Infectious Myositis Causes and Treatment

Infectious myositis is an acute, subacute, or chronic infection of skeletal muscle. It was considered a tropical disease once but  is now seen in temperate climates as well, particularly with the emergence of HIV infection.

Viruses, bacteria (including mycobacteria), fungi, and parasites can cause infectious myositis.

Infectious myositis has a male predominance and is typically seen in young adults. Single or multiple muscle groups in the limbs can be involved. Trichinosis commonly involves orbital muscles.

Causes of Infectious Myositis

Known pathogens include the following:

Viral

• HIV-1 (one of the most common causes of myositis)
• HTLV-1
• Cytomegalovirus
• group B coxsackievirus (epidemic myalgia)
• influenza

Bacterial

• S aureus (most common, 70%)
• Streptococcus group
• Salmonella enteritidis
• Klebsiella pneumonia
• Clostridium freundii
• Bartonella
• gram-negative organisms
• Escherichia coli
• Pseudomonas aeruginos
• Neisseria species
• Yersinia species
• Morganella morganii
• Citrobacter species

Parasitic

• Trichinella
• Echinococcus granulosus
• T solium, T cruzi

Fungal

• Cryptococcus neoforman
• Candida species
• Histoplasma capsulate
• Coccidioides specie
• Aspergillus species
• Pneumocystis jiroveci
• Microsporidia Fusarium species
• Actinomyces species;
• Mucormycosis
• Sporothrix schenckii
• Blastomyces dermatitidis

Spirochetal

B burgdorferi

Mycobacterial

Mycobacterium avium-intracellulare complex

Common Types of Infectious Myositis

Viral Myositis

Viruses implicated include HIV-1, human T lymphotrophic virus 1 (HTLV-1), influenza, coxsackieviruses, and echoviruses. The viral polymyositis is most likely autoimmune in origin. Influenza myositis could be due to direct viral invasion or autoimmune response.

 Influenza Virus

In children, this condition occurs after an episode of fever, malaise, and rhinorrhea followed by severe pain, especially in the calves that coincides with subsidence of fever. The muscle pain worse with movement, especially with walking. It is also know as benign acute myositis and is a self limiting condition that generally last 1-7 days.

In adults, there would be fever myalgias and generalized weakness. Muscle swelling may occur in some patients.

Complications include myocarditis and respiratory dysfunction.

Coxsackie Virus

Group A virus can cause an acute, diffuse inflammatory myopathy that may progresses to rhabdomyolysis and myoglobinuria. Renal failure may be a complicationleading to renal failure.

Group B virus infection causes severe pain in the muscles between the ribs or in the diaphragm [pleurodynia, also called Bornholm disease or epidemic myalgia.

It is  an acute, febrile disorder with abrupt onset of pain in the abdomen or lower thoracic region. Pain can be referred to the back and shoulders and is worse on movements,  breathing, or coughing.

Muscle tenderness and swelling may be noted in some patients.

Pyomyositis or Bacterial Myositis

Trauma, viral infection, and malnutrition have been implicated as the causes. Nutritional deficiency and associated parasitic infection in tropical climates may contribute. In the temperate climates, pyomyositis is seen most commonly in patients with diabetes, HIV infection, and malignancy.

Staphylococcus Pyomyositis

The affected muscles are painful, swollen, tender, and indurated. Quadriceps muscle is the most common muscle involved followed by the psoas muscle, and then the upper extremities.

This may be difficult to distinguish clinically from inflammatory myopathy.

Findings may be subtle in immunocompromised persons.

Streptococcal Pyomyositis

Most common form is group A streptococci  necrotizing myositis/streptococcal myonecrosis which is usually seen in the men and young adults. It is seen in the immunocompromised patients and is characterized by flulike symptoms which evolve to severe local muscle pain, swelling, and fever. It may be rapidly progressive and can be fatal due to toxic shock syndrome, multiorgan failure.

Lyme Borreliosis

The disease is transmitted by the bites of ticks of the Ixodes genus that carry the spirochete. Lyme disease may cause myositis by invasion of muscle by the spirochete Borrelia burgdorferi or by autoimmune mechanisms.

It is characterized  by pain and weakness of the proximal muscle groups in the  vicinity of skin lesions. Local tenderness, swelling  and wasting of muscles may be seen.

Late ocular involvement may cause orbital myositis.

Parasitic Myositis

Trichinosis

It is characterized by myalgia, periorbital swelling, and fever. Depending on the site of involvement, the features may be diplopia, dysarthria, dysphagia and. Mild involvement of limb muscles may be noted.

Myocarditis may occur.

Cysticercosis

It is an infection by the larval stage of the intestinal tapeworm Tenia solium. It is transferred from pigs to human by ingestion of raw or incompletely cooked pork. Another mode of infection is by contamination of food and water by feces containing the eggs of the tapeworm. The larvae migrate throughout the body and may form fluid-filled cysts in a variety of tissues, including muscle.

The most common sites of involvement are the skeletal and cardiac muscle, brain, and eyes.

When skeletal muscles are involved, palpable cysticerci (mature larvae) appear in subcutaneous tissues.

A notable feature of this type of myositis is muscle pseudohypertrophy.

During the acute stage of disease, patients may have fever and muscle tenderness.

Fungal Myositis

• Most often seen in severely immunosuppressed patients
• Clinical presentation is similar to pyomyositis
• Often present with lower extremity pain and swelling
• May involve the paraspinal musculature
• Clinically presents with fever, rash, and muscle tenderness

Toxoplasma myositis

It is caused by Toxoplasma gondii  and usually is seen in immunocompromised individuals with disseminated toxoplasmosis.

Clinical features are similar to those of polymyositis, with manifestations of fever and muscle weakness.

Clinical Presentation

The clinical features are given in individual description. The patient should be enquired for

• Risk factors for Staphylococcus aureus pyomyositis
  • Strenuous activity
  • Muscle trauma
  • Skin infections
  • Infected insect bites
  • Drugs via injection
  • Connective tissue disorders
  • Diabetes
• Overseas travel
• Consumption of poorly cooked meats
• Tick bites

Differential Diagnoses

• Neuropathies
  • inflammatory Demyelinating Polyradiculoneuropathy
  • Femoral Mononeuropathy
  • Paraneoplastic Autonomic Neuropathy
• Metabolic Myopathies
• Neuromuscular and Myopathic Complications of HIV
• Polymyositis

Lab Studies

Routine Tests

Following lab tests are done

• CBC
• ESR
• CRP
• Biochemistry

Leucocytosis is seen  in pyomyositis. Trichinosis and other parasitic infections may show eosinophilia. ESR and CRP is increased across all the types.

• Muscle enzyme levels are increased.
• IgE levels are increased in parasitic infections.
• Lyme antibody titre may be done using ELISA in suspected cases. Similarly Toxoplasma antibodies titre would be raised in myositis caused by toxoplasma.
• Viral serology for suspected viral cases.
• Muscle biopsy in cryptococcal myositis may reveal intracytoplasmic organisms
• Fungal stain and culture may be done to identify fungal cause

Aspiration, Stain and Pyomyositis

Needle aspiration is useful for the detection of purulent material and for microbiologic identification of the causative organism.

Histopathological Findings

Histopathological findings differ according to the cause of myositis. Inflammation and/or necrosis is seen across all the etiologies.

Characteristic features are

Trichinosis

• Interstitial infiltrates composed mainly of eosinophils
• Trichinella species larvae or encapsulated cysts may be visible
• Focal calcification

Pyomyositis

• Widespread necrosis
• Pleomorphic inflammatory response

Streptococcal myositis

Muscle necrosis and gram-positive bacteria in chains is noted.

Cysticercosis

Little or no tissue reaction.

Ruptured cyst  – acute inflammatory response with a pleomorphic exudate

Lyme myositis

• Atrophic fibers
• and an infiltrate consisting of lymphocytes, plasma cells, and macrophages.
• Borrelia burgdorferi can be detected

Viral myositis

• Muscle fiber necrosis without inflammatory
• Viral particles can be identified in muscle fibers under electron microscopy.
• Inflammatory response consisting of mononuclear and polymorphonuclear leukocytes.
• Muscle fiber regeneration may be seen

Fungal myositis

Characteristic fungal appearances may be seen

Imaging Studies

MRI

MRI is the image of choice in myositis. MRI is able to differentiate pyomyositis or tuberculous abscess from osteomyelitis. It also differentiates early muscle inflammation from abscess formation.

Godlinium enhncaced MRI is used to identify tuberculosis.

MRI is able to identify cysticercosis with orbital involvement

In trichinosis MRI, may show a clear cyst with a scolex [also can be seen on CT and ultrasound]

MRI can distinguish between tumors and hematomas from abscess.

CT

Calcifications are best visualized on CT scans. CT scanning may show hypertrophy of involved muscle groups and effacement of the fat planes. Contrast enhancement may indicate abscess formation.

Nuclear Scan

Gallium scan is useful for localization in the early stages of illness.

Electromyography

Viral polymyositis

Features are similar to idiopathic polymyositis.

• Short-duration motor unit potentials
• Low-amplitude polyphasic motor unit potentials
• Fibrillations

Trichinosis

EMG may reveal fibrillation potentials.

Lyme myositis

Changes of denervation may be seen in the involved muscles.

Treatment of Infectious Myositis

Exact treatment would depend on the diagnosis. Rest and medication are mainstay of the treatment. The drugs given in a particular case would depend on the diagnosis and causative agents.

Viral Myositis

• Treatment comprises bed rest, intravenous fluids, and symptomatic management with antipyretics and analgesics.
• Antiviral agents such as amantadine could be considered in adults.
• HIV- corticosteroids

Trichinosis

Thiabendazole is effective if administered within 24 hours of infection but less effective in established infection.

Pyomyositis

• Antibiotics depending on the  causative organisms
• Abscess drainage if required

Myobacterial

Antitubercular chemotherapy

Fungal myositis

A antifungal agent such as amphotericin B.

Complications

Complications are varied and depend on the type of myositis

For example rhabdomyolysis may be sen in viral type.

Pyomyositis can be complicated by sepsis and toxic shock syndrome.

Gas gangrene may occur in clostridial pyomyositis.

Myocarditis and/or diaphragmatic involvement in trichinosis.

Prevention of Myositis

• Prevent trichinosis and cysticercosis by adequately processing pork.
• Protection from insects by using repellents, insect killers or bed nets.

References

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• Costa RM, Dumitrascu OM, Gordon LK. Orbital myositis: diagnosis and management. Curr Allergy Asthma Rep. 2009 Jul. 9(4):316-23.
• Trusen A, Beissert M, Schultz G, et al. Ultrasound and MRI features of pyomyositis in children. Eur Radiol. 2003 May. 13(5):1050-5.
• Crum-Cianflone NF. Bacterial, fungal, parasitic, and viral myositis. Clin Microbiol Rev. 2008 Jul. 21(3):473-94.
• Crum-Cianflone NF. Nonbacterial myositis. Curr Infect Dis Rep. 2010 Sep. 12(5):374-82..
• Patel SR, Olenginski TP, Perruquet JL, Harrington TM. Pyomyositis: clinical features and predisposing conditions. J Rheumatol. 1997 Sep. 24(9):1734-8.