Introduction

What do a tropical traveller, a diabetic patient, and a heroin user have in common? They are all at risk of developing a rare, serious muscle infection called pyomyositis. Pyomyositis is an infection of the skeletal muscle, characterised by a collection of pus in skeletal muscles, manifesting as single or multiple abscesses.¹ You may have heard of staph infections, but did you know that they can also affect your muscles?

Pyomyositis is a bacterial infection that results in localised abscess formation, most frequently caused by Staphylococcus aureus.^2–4 Pyomyositis is more frequently reported in tropical countries, but it has been diagnosed over a wide range of ages, from 2 weeks to 92 years.⁵

Causes

The cause of pyomyositis is multifactorial, with various etiological agents and risk factors contributing to its development. Staphylococcus aureus is a predominant cause, and other bacterial, fungal, and parasitic agents, as well as systemic diseases, trauma, and myopathy, can also play a role in the pathogenesis of pyomyositis.

 Pyomyositis may originate from a focal infection such as arthritis, sacroiliitis, a spinal abscess, bacteremia, or sepsis.⁶ The condition is thought to be caused by seeding from transient bacteremia, which is nearly always caused by Staphylococcus aureus.^7,8

Additionally, damaged muscles from trauma (injection drug use or contact sports), mitochondrial damage from drug toxicity, and myopathy are major risk factors for pyomyositis.⁹ Furthermore, primary pyomyositis is due to transient bacteremia as the major cause, while secondary pyomyositis can occur from contiguous infectious spread from osteomyelitis or cellulitis.¹⁰

The described bacterial etiologic agents of pyomyositis include Staphylococcus aureus, Escherichia coli, and other bacteria.^5,11–13 Additionally, tuberculosis has been identified as a cause of pyomyositis, with reported cases of tuberculous pyomyositis.¹⁴ Furthermore, B. dermatitis has been identified as a potential cause of classic pyomyositis.¹⁵ Parasites such as toxocara and leptospiral infections have also been implicated as predisposing infectious causes of pyomyositis.¹⁶

Symptoms

Pyomyositis, a life-threatening bacterial infection of the skeletal muscle, can affect individuals of various age groups, including children, young adults, and immunocompromised individuals.¹⁷ It has been associated with factors such as strenuous exercise, direct muscle trauma, and immune deficiencies, with an increasing prevalence of conditions like diabetes mellitus and HIV/AIDS in the adult population.^18,19

The infection typically presents with symptoms such as fever, localised abscess, and muscle pain, and it predominantly affects muscle groups in the pelvis, including the obturator internus, externus, adductors, gluteus maximus, minimus, medius, piriformis, and iliopsoas.²⁰ Additionally, pyomyositis can manifest as hip pain, which should be considered in the differential diagnosis, especially in adults.²¹ The condition is primarily caused by Staphylococcus aureus, and it is essential to consider pyomyositis when immunocompetent adults present with apparently idiopathic inflammatory muscle lesions.⁸

Furthermore, pyomyositis has been reported in individuals with systemic lupus erythematosus and has been associated with muscle inflammation and corticosteroid use as possible predisposing factors.^22,23 The incidence of pyomyositis is on the rise worldwide among both children and adults, and it is crucial to recognise its atypical presentations, such as in the neck, extraocular muscles, and obturator internus, to ensure timely diagnosis and management.^24–26

Diagnosis

The diagnosis of pyomyositis in adults can be challenging due to its rare occurrence, varied clinical manifestations, and atypical symptoms. Computed tomography has been noted to show areas of low attenuation with loss of muscle planes and a surrounding rim of contrast enhancement as characteristic of pyomyositis.¹ Additionally, a delay in diagnosis can lead to serious complications, including multiple abscess formation, septicemia, multi-organ system failure, and occasionally death.³

The aetiology of pyomyositis is often unclear, but risk factors associated with the condition include immunosuppression, strenuous exercise, and direct muscle trauma.²⁷ In the emergency department, diagnosing pyomyositis can be particularly challenging, especially when patients present with atypical symptoms such as fever with hip, back, or flank pain, especially in patients who are difficult to manage, such as intravenous drug users.¹⁰

Furthermore, the diagnosis of pyomyositis affecting the deep muscles of the back and pelvis can be missed in patients with a background history of chronic back pain and sciatica.²⁸ The rarity and indolent presentation of pyomyositis often lead to findings comparable to other conditions, such as deep vein thrombosis, septic arthritis, avascular necrosis, diabetic amyotrophy, and cellulitis, making the diagnosis difficult.²⁹

Treatment

The treatment of pyomyositis involves a multidisciplinary approach, including surgical drainage and antibiotic therapy. Prompt and appropriate management is essential to prevent the progression of the infection and the development of complications and to ensure favourable patient outcomes.

Treatment of pyomyositis typically involves a combination of surgical drainage and antibiotic therapy. Surgical drainage, either through incision and drainage or guided aspiration, is often necessary to evacuate the abscess and reduce the bacterial load within the affected muscle.^30,31 This approach is crucial in preventing the progression of the infection and the development of complications such as abscess formation and septic shock.^32,33

Additionally, broad-spectrum empirical antibiotics are recommended initially in treating pyomyositis, and the beta-lactam class of antibiotics is frequently used for this purpose.³⁴ Intravenous antibiotics are typically administered to ensure adequate tissue penetration and systemic medication delivery.⁵ The choice of antibiotics should be guided by the suspected causative pathogen and its sensitivity profile, which can be determined through culture and sensitivity testing.³⁵

It is important to note that successful treatment of pyomyositis abscesses with antibiotics alone has been reported in some cases. However, this approach is less common and typically reserved for select cases.³⁰ However, surgical drainage is often necessary to ensure effective resolution of the infection in the presence of a muscle abscess, especially in an immunocompromised patient.³¹

Prevention

Preventing pyomyositis involves a multifaceted approach, including avoiding overexertion, early recognition and treatment of minor muscle injuries, closely monitoring high-risk individuals, and addressing malnutrition in at-risk populations. These measures can contribute to reducing the incidence and impact of pyomyositis.

Preventing pyomyositis involves addressing risk factors and promoting measures to reduce the likelihood of infection. Pyomyositis has been associated with factors such as strenuous exercise and direct muscle trauma, highlighting the importance of avoiding overexertion and ensuring proper muscle care to minimise the risk of muscle-related infections.³⁶

Additionally, early recognition and treatment of minor muscle injuries can help prevent the progression of localised trauma to pyomyositis.³⁷ In children, the consideration of pelvic osteomyelitis or pyomyositis in the presence of signs of infection and the absence of a hip effusion is crucial for early diagnosis and management.³⁸ Furthermore, prompt recognition of pyomyositis is necessary for proper treatment and prevention of complications such as sepsis, chronic osteomyelitis, and even death.³⁹

In high-risk individuals, such as those with systemic conditions like diabetes mellitus and immunodeficiency or those undergoing chemotherapy, close monitoring and proactive measures to prevent infections are essential.⁴⁰ Additionally, addressing malnutrition, which has been described as a risk factor for developing pyomyositis, is crucial in populations where malnutrition is prevalent.⁴¹ Furthermore, eliminating nasal carriage of Staphylococcus aureus with topical mupirocin formulation has been suggested as a preventive measure.⁴²

FAQs

What is pyomyositis, and who is at risk of developing it?

Pyomyositis is a rare bacterial infection of the skeletal muscle characterised by pus collection within muscles. Individuals at risk include travellers to tropical regions, diabetics, heroin users, and those with conditions causing immune deficiency.

What are the common symptoms of pyomyositis, and how does it typically present?

Pyomyositis often presents with symptoms such as fever, localised abscess, and muscle pain. It predominantly affects muscle groups in the pelvis, including the obturator internus, externus, adductors, gluteus maximus, minimus, medius, piriformis, and iliopsoas.

How is pyomyositis diagnosed, and what challenges are associated with its diagnosis?

Diagnosis of pyomyositis can be challenging due to its rare occurrence and varied clinical manifestations. Computed tomography may reveal areas of low attenuation with loss of muscle planes and contrast enhancement. Atypical symptoms and findings may lead to misdiagnosis or delayed diagnosis, often resembling other conditions such as deep vein thrombosis or cellulitis.

What is the recommended treatment for pyomyositis, and why is prompt intervention crucial?

Treatment typically involves surgical drainage and antibiotic therapy. Prompt intervention is essential to prevent complications such as multiple abscess formation, septicemia, multi-organ system failure, and death. Surgical drainage helps evacuate the abscess and reduce bacterial load within the affected muscle, while antibiotics target the causative pathogens.

How can pyomyositis be prevented, and how can individuals reduce their risk?

Prevention strategies include avoiding overexertion, early recognition and treatment of minor muscle injuries, and close monitoring of high-risk individuals such as those with diabetes or immunodeficiency. Addressing malnutrition and considering nasal carriage of Staphylococcus aureus as preventive measures can further reduce the risk of infection.

Summary

If you think muscle pain is a pain in the neck, wait until you hear about pyomyositis. This rare infection causes pus-filled abscesses in your muscles, usually in your legs. It can be hard to diagnose, as it can mimic other conditions like blood clots, tumours, or appendicitis. You need blood tests, imaging studies, and sometimes a muscle biopsy to confirm it. The treatment involves antibiotics, draining the abscess, and supportive care. The outcome depends on how quickly you get treated and whether you have any complications. Pyomyositis is not a walk in the park, but it can be managed with proper care.