eMedicine Specialties > Neurology > Neurological Infections

Infectious Myositis

Author: Mohammed J Zafar, MD, FAAN, Associate Clinical Professor of Medicine, Kalamazoo Center for Medical Studies, Michigan State University; NeuroImager, Premier Medical Care, PC, Premier Radiology, Kalamazoo Neurologic Institute
Contributor Information and Disclosures

Updated: Aug 12, 2009

Introduction

Background

Infectious myositis is an acute, subacute, or chronic infection of skeletal muscle. Once considered a tropical disease, it is now seen in temperate climates as well, particularly with the emergence of HIV infection.^1,2 In addition to HIV, other viruses, bacteria (including mycobacteria), fungi, and parasites can cause myositis. For a detailed discussion of HIV-associated myopathies, refer to eMedicine article HIV-1 Associated Myopathies.

Pathophysiology

Single or multiple muscle groups in the limbs can be involved, a notable exception being trichinosis, which commonly involves orbital muscles. In most instances, involvement of proximal muscles is predominant. Characteristic myopathic features and findings of polymyositis, including inflammatory infiltrates, may be seen.

Viruses: Viruses implicated in the pathogenesis of myositis include HIV-1, human T lymphotrophic virus 1 (HTLV-1), influenza, coxsackieviruses, and echoviruses. As in the non–HIV-infected population, HIV-associated polymyositis is most likely autoimmune in origin. Influenza myositis could be due to direct viral invasion or autoimmune response.

Pyomyositis: The pathogenesis is unclear, but trauma, viral infection, and malnutrition have been implicated. Although most cases of tropical pyomyositis occur in healthy individuals, other pathogenetic factors include nutritional deficiency and associated parasitic infection. In the temperate climates, pyomyositis is seen most commonly in patients with diabetes, HIV infection, and malignancy.

Lyme borreliosis: Musculoskeletal manifestations are noted frequently in Lyme borreliosis. The disease is transmitted by the bites of ticks of the Ixodes genus that carry the spirochete (see Media file 1). The animal reservoirs are the white-footed mouse in the Eastern United States and the wood rat in California. Human infection results from the bite of infected ticks in the late spring and early summer. Lyme myositis may result from direct invasion of muscle by the spirochete Borrelia burgdorferi or by autoimmune mechanisms.³

Cysticercosis: Myositis also can occur in cysticercosis, which represents an infection by the larval stage of the intestinal tapeworm Taenia solium. Human infection results from 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.

Frequency

United States

• Pyomyositis: Approximately 676 cases have been reported in the US literature since 1971.
• Lyme disease: Endemic areas include the Northeast, mainly Connecticut, Massachusetts, Maryland, and New York; the North-Central region, mainly Wisconsin and Minnesota; and the West Coast, especially Northern California.

International

• In eastern Uganda, 400-900 cases of tropical myositis occur per year; it is rare in western Kenya.
• Cysticercosis is most prevalent in India, Eastern Europe, Central America, and Mexico.
• In endemic areas of Latin America, 8% of the population is seropositive for American trypanosomiasis.

Mortality/Morbidity

• A potentially life-threatening complication of pyomyositis is toxic shock syndrome.
• Rhabdomyolysis can complicate influenza and, rarely, coxsackievirus myositis.

Race

• In Hawaii, muscle abscesses were noted to be confined to the Polynesians.
• In the French Pacific islands, the disease is not seen in the French settlers.

Sex

Infectious myositis has a male predominance.

Age

Infectious myositis typically is seen in young adults.

Clinical

History

• Key historical points should be confirmed.
  • Risk factors for Staphylococcus aureus pyomyositis - Strenuous activity, muscle trauma, skin infections, infected insect bites, illicit drug injections, connective tissue disorders, and diabetes
  • Overseas travel
  • Consumption of poorly cooked meats (especially pork products in the case of trichinosis or cysticercosis)
  • Tick bites
• Pyomyositis
  • Fever and malaise
  • Psoas abscess - Subtle symptoms such as fever and flank and hip pain; may manifest as pyrexia of unknown origin
• Trichinosis
  • Cardinal features - Myalgia, periorbital swelling, and fever (see Media file 3)
    
    

    

    A patient with trichinosis and ocular involvement. Courtesy of Centers for Disease Control and Prevention and Dr. Thomas F. Sellers, Jr.

    [ CLOSE WINDOW ]

    

    A patient with trichinosis and ocular involvement. Courtesy of Centers for Disease Control and Prevention and Dr. Thomas F. Sellers, Jr.

  • Depending on site of involvement - Diplopia, dysarthria, dysphagia, dyspnea
• Lyme myositis
  • Pain and weakness of the proximal muscle groups
  • Symptoms in the vicinity of skin lesions or in limb muscles
• Cysticercosis with myositis - Fever, myalgias
• Trypanosomiasis with myositis
  • Acute stage
    • May be asymptomatic or characterized by fever
    • Myositis occurring in the early stage of infection - Symptoms such as muscle weakness and myalgias mimicking those of polymyositis
  • Chronic stage - Myalgias
• Toxoplasma myositis - Fever, myalgias, and muscle weakness
• Influenza myositis - Childhood and adult forms recognized
  • Childhood form
    • Fever, malaise, and rhinorrhea followed 1-7 days later by severe pain, especially in the calves
    • Muscle pain worse with movement, especially with walking
    • Symptoms of myositis - Generally last 1-7 days
  • Adult form
    • Fever, myalgias, generalized weakness
    • Muscle swelling in some patients
• Acute coxsackievirus myositis
  • Group A virus infection - Myalgias, weakness
  • Group B virus infection - Causes epidemic pleurodynia (Bornholm disease or epidemic myalgia), which is considered a form of myositis
    • This 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.
    • Pain is worse with movement, breathing, or coughing.

Physical

• Pyomyositis
  • Muscles are painful, swollen, tender, and indurated.
  • Quadriceps muscle is involved most commonly.
  • The second most common location is the psoas muscle, followed by the upper extremities.
  • Depending on the site of involvement, it may mimic appendicitis (psoas muscle), septic arthritis of the hip (iliacus muscle), or epidural abscess (piriformis muscle).
  • This may be difficult to distinguish clinically from inflammatory myopathy. 
  • Findings may be subtle in immunocompromised persons requiring a high index of suspicion for diagnosis.
• Trichinosis
  • Involvement of orbital muscles can result in diplopia and strabismus.
  • Dysarthria or dysphagia can result when tongue and pharyngeal muscles are affected.
  • Limb muscles usually are mildly involved.
  • Other manifestations include myocarditis and dyspnea from diaphragmatic involvement.
• Lyme myositis
  • Weakness and atrophy of the proximal muscle groups can occur, accompanied by local swelling and tenderness.
  • Muscle weakness may be a major presenting feature of this disease.
  • Rarely, late ocular involvement, including orbital myositis⁴ , may occur.
• Cysticercosis with myositis
  • 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, which may be seen in the tongue or calf muscles.
  • During the acute stage of disease, patients may have fever and muscle tenderness.
• Trypanosomiasis with myositis
  • The acute stage of the disease may be characterized by fever, lymphadenopathy, and hepatosplenomegaly.
  • At the site of the insect bite, local inflammation (involving subcutaneous tissues and muscle) results in a swelling known as a chagoma.
  • Contamination of the eyes produces unilateral periocular and palpebral edema with conjunctivitis and preauricular lymphadenopathy (Romaña).
  • Extraocular involvement is rare. It may present with features of subacute orbital myositis and may mimic an orbital tumor.
  • During the acute parasitemic stage, intense infection of the myocardium may occur, producing severe myocarditis and disturbances of cardiac conduction.
  • Clinical manifestations in the early stage of myositis include muscle weakness, tenderness, and erythema mimicking those of polymyositis and dermatomyositis.
  • Skeletal muscle may be involved in the chronic stage as well and can last for decades.
• Toxoplasma myositis
  • Muscle invasion by Toxoplasma gondii usually is seen in immunocompromised individuals with disseminated toxoplasmosis.
  • The clinical features are similar to those of polymyositis, with manifestations of fever and muscle weakness.
  • Polymyositis is a prominent feature even in the congenital form of toxoplasmosis.
• Influenza myositis
  • Muscle weakness, tenderness, and swelling
    • More severe in adults
    • Proximal muscles are affected predominantly.
    • In children, involvement of the gastrocnemius-soleus muscles causes calf pain and difficulties with walking( toe-walking, wide-based gait)
    • Complications include myocarditis and respiratory dysfunction.
• Acute coxsackievirus myositis
  • Group A virus
    • These viruses can cause an acute, diffuse inflammatory myopathy.
    • This may progress to rhabdomyolysis and myoglobinuria, leading to renal failure.
  • Group B virus infection (epidemic myalgia)
    • Muscle tenderness and swelling may be noted in some patients.
    • Relapses can occur 2 weeks to a few months after the initial presentation.

Causes

HIV infection is one of most important causes of viral myositis. Opportunistic infections can cause myositis in immunosuppressed patients. Known pathogens include the following:

• Viral - HIV-1, HTLV-1, cytomegalovirus, group B coxsackievirus (epidemic myalgia), influenza
• Bacterial -S aureus (most common, 70%); Streptococcus viridans; Streptococcus pyogenes; Streptococcus pneumoniae⁵ ; Salmonella enteritidis; Klebsiella pneumoniae; Clostridium freundii; Bartonella; gram-negative organisms including Escherichia coli and Pseudomonas aeruginosa, Neisseria, Yersinia, Morganella morganii, and Citrobacter species
• Spirochetal -B burgdorferi
• Mycobacterial -Mycobacterium avium-intracellulare complex
• Parasitic -T gondii, Trichinella spiralis, Echinococcus granulosus, T solium, T cruzi, microsporidia
• Fungal - Cryptococcus, actinomyces

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