Infectious Myositis Clinical Presentation

Updated: Jan 13, 2018
  • Author: Mohammed J Zafar, MD, FAAN, FACP, FASN; Chief Editor: Niranjan N Singh, MBBS, MD, DM, FAHS, FAANEM  more...
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See the list below:

  • 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
    • Psoas abscess - Subtle symptoms such as fever and flank and hip pain; may manifest as pyrexia of unknown origin; may be primary (no identifiable source of infection/from occult hematogenous spread) or secondary (spread from infection in the vicinity)
    • Occur mostly in the immunocompromised
    • Fever and malaise
  • Streptococcal myositis
    • Most common form is group A streptococci (GAS) necrotizing myositis/streptococcal myonecrosis
    • Usually seen in the men and young adults
    • Spontaneous occurrence (no history of penetrating trauma) or in the immunocompromised
  • Trichinosis
    • Cardinal features - Myalgia, periorbital swelling, and fever (see following image)
      A patient with trichinosis and ocular involvement. 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.
  • Fungal myositis
    • Most often seen in severely immunosuppressed patients
    • Clinical presentation is similar to pyomyositis
  • Cryptococcal myositis
    • Rare cause of myositis
    • Most involve immunocompromised patients.
    • Symptoms overlap those of bacterial myositis.
    • Often present with lower extremity pain and swelling
    • May involve the paraspinal musculature


See the list below:

  • 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.
  • Streptococcal myositis
    • Prodrome - Flulike symptoms
    • Evolves to severe local muscle pain, swelling, and fever
    • Rapidly progressive and can be fatal
    • Complications - Bacteremia, toxic shock syndrome, multiorgan failure
  • 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 myositis [4] , 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 [5, 6]
    • 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.
  • Fungal myositis
    • Clinically presents with fever, rash, and muscle tenderness
    • Lower extremities are commonly involved.


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 viridans; Streptococcus pyogenes; Streptococcus pneumoniae [7] ; Salmonella enteritidis; Klebsiella pneumoniae; Clostridium freundii; Bartonella; gram-negative organisms including Escherichia coli, Pseudomonas aeruginosa, Neisseria species , Yersinia species , Morganella morganii, and Citrobacter species
  • Spirochetal - B burgdorferi
  • Mycobacterial - Mycobacterium avium-intracellulare complex
  • Parasitic - T gondii, Trichinella spiralis, Trichinella nativa (from eating bear meat), T nelsoni, T britovi, T pseudospiralis, Echinococcus granulosus, T solium, T cruzi, microsporidia
  • Fungal - Cryptococcus neoformans, Candida species (especially Candida tropicalis, Candida krusei, Candida albicans) , Histoplasma capsulatum, Coccidioides species , Aspergillus species , Pneumocystis jiroveci, microsporidia (eg, Anncaliia algerae [8] ), Fusarium species, and Actinomyces species; less common are mucormycosis, Sporothrix schenckii, and Blastomyces dermatitidis