What is myonecrosis?

What is Myonecrosis

Myonecrosis is the death (necrosis) of muscle tissue, most commonly caused by bacterial infection—particularly clostridial gas gangrene—but also occurring from non-infectious causes including trauma, vascular compromise, and metabolic conditions.

Infectious Myonecrosis

Clostridial Myonecrosis (Gas Gangrene)

Clostridial gas gangrene represents the most severe and rapidly progressive form of infectious myonecrosis, primarily caused by Clostridium perfringens, with C. novyi, C. histolyticum, and C. septicum as less common pathogens 1.

Clinical Presentation

• Increasingly severe pain beginning at the injury site 24 hours after infection is the first reliable symptom 1
• Skin progression follows a characteristic pattern: initially pale → bronze → purplish red 1
• The infected region becomes tense and tender with bullae filled with reddish-blue fluid 1
• Gas in tissue (detected as crepitus or on imaging) is universally present by late stages 1
• Systemic toxicity develops rapidly: tachycardia, fever, diaphoresis, followed by shock and multiple organ failure 1

Two Distinct Subtypes

Traumatic gas gangrene is associated with C. perfringens and occurs following severe penetrating trauma or crush injuries with vascular compromise 1, 2.

Spontaneous gangrene is principally associated with the more aerotolerant C. septicum and occurs in patients with neutropenia and gastrointestinal malignancy 1. It develops in normal skin without trauma via hematogenous spread from a colonic lesion (usually cancer), with an innocuous early lesion evolving to full manifestations over 24 hours 1.

Pathophysiology

• Clostridial species produce multiple toxins (alpha, theta, beta) that induce cellular apoptosis and severe immunological conditions 2
• C. perfringens alpha toxin (CPA) hydrolyzes sphingomyelin and phosphatidylcholine in plasma membranes, triggering necrosis and apoptosis 2
• The bacteria possess over 200 transport-related genes facilitating nutrient uptake in anaerobic host environments 2

Diagnosis and Management

• Early surgical inspection and debridement are necessary 1
• Gram stain of removed tissue shows large, spore-forming gram-positive bacilli 1
• For severe clostridial necrotizing infections, parenteral clindamycin and penicillin treatment is recommended 1
• Hyperbaric oxygen therapy is considered adjunctive treatment to inhibit anaerobic bacterial growth and enhance antibiotic efficacy 2

Anaerobic Streptococcal Myositis

This represents a more indolent infection compared to clostridial myonecrosis 1. Unlike other necrotizing infections, anaerobic streptococcal muscle and fascial plane infections are usually associated with trauma or surgical procedures 1.

Management differs critically from clostridial infections:

• Incision and drainage are critical, with resection of necrotic tissue and debris 1
• Inflamed, viable muscle should NOT be removed, as it can heal and regain function 1
• All organisms are susceptible to high-dose penicillin or ampicillin 1

Bacterial (Pyogenic) Myositis

• Blood cultures are positive in 5-30% of cases 1
• Staphylococcus aureus accounts for approximately 70% of bacterial myositis cases 3
• Vancomycin is recommended as initial empirical therapy 3
• Standard antibiotic duration is 2-3 weeks, with transition from IV to oral when clinically improved 3

Non-Infectious Myonecrosis

Trauma-Related Myonecrosis

Calcific myonecrosis is a rare late complication of limb trauma characterized by liquefaction and dystrophic calcification of muscles in a single compartment, usually occurring many years after the initial injury 4, 5.

Pathophysiology and Presentation

• Develops several decades after lower extremity trauma typically associated with vascular injury 5
• Likely results from chronic compartment syndrome 4
• Presents as a painful, expansile, calcified mass replacing leg musculature 5
• The pathologic findings suggest expansion over time via recurrent intralesional hemorrhage into a chronic calcified mass 5

Imaging Characteristics

• Plain radiographs show well-defined, heavily calcified mass with thin, linear calcifications organized around the periphery 5
• MRI shows heterogeneous signal with enhancement limited to the periphery 5
• Smooth erosion of adjacent bone may be present 5

Management Considerations

• Surgical intervention is associated with high complication rates, particularly with intralesional procedures 5
• Thorough debridement of the involved compartment with limited access dressing may be an option, though morbidity from extensive debridement persists 4

Radiation-Induced Myonecrosis

In oncology patients, myonecrosis is most frequently associated with radiotherapy (45% of cases) 6.

Other causes in this population include:

• Intraoperative immobilization 6
• Therapeutic embolization 6
• Ablation therapy 6
• Exercise and diabetes 6

The "stipple sign" (enhancing foci within a region defined by rim enhancement) may be observed on MRI, though interobserver variability exists 6.

Metabolic and Vascular Myonecrosis

Sickle Cell-Related Myonecrosis

• Red cells containing sickle hemoglobin become rigid, resulting in reduced blood flow and myonecrosis 7
• Early recognition is critical, allowing for prompt and aggressive fluid resuscitation, which remains a cornerstone in management 7
• MRI shows low intensity signal on T1 and high intensity signal on T2 at the affected muscle belly 7
• In actively sickling patients, any invasive intervention should be avoided as it can result in ischemic necrosis due to interruption of capillary flow in end-arteries 7

Nerve Agent-Induced Myonecrosis

• Severe myonecrosis can result from excessive acetylcholine accumulation in the synaptic cleft during nerve agent poisoning 1
• Calcium overload causes myocyte death with subsequent rhabdomyolysis potentially causing renal damage 1
• Close monitoring of serum creatine kinase and potassium is advised to prevent myoglobinuric renal failure 1

Myocardial Myonecrosis

In the cardiac context, myonecrosis refers to myocardial cell death detected by elevated cardiac biomarkers (preferably troponin levels above the 99th percentile) 1. This represents a distinct entity from skeletal muscle myonecrosis and requires differentiation from myocardial injury caused by non-ischemic conditions 1.

Critical Clinical Pitfalls

• Do not delay surgical exploration when necrotizing infection is suspected—early debridement is life-saving 1
• Distinguish between clostridial myonecrosis (remove all necrotic tissue) and anaerobic streptococcal myositis (preserve viable inflamed muscle) 1
• Recognize spontaneous gas gangrene in neutropenic patients with GI malignancy—it occurs without trauma 1
• In calcific myonecrosis, surgical intervention carries high complication rates; conservative management should be strongly considered 5
• Repeat imaging is mandatory in patients with persistent bacteremia to identify undrained collections 3, 8