Myotoxins

Myotoxins are substances that directly damage skeletal muscle tissue or disrupt its function, leading to myopathy or rhabdomyolysis. They can arise from external sources such as venomous animals or bacteria, or from endogenous disease processes. In venom, myotoxic proteins—particularly phospholipases A2 and related peptides found in many viperid and some elapid venoms—injure muscle fibers by disrupting cell membranes, disturbing calcium homeostasis, and triggering inflammatory responses. Bacterial toxins can also act as myotoxins; for example, Clostridium perfringens alpha-toxin promotes myonecrosis and gas gangrene through phospholipase activity and membrane damage.

Clinical features typically include sudden muscle pain, swelling, and weakness, often in proximal muscles, with dark urine from myoglobin release if rhabdomyolysis occurs. Laboratory findings include markedly elevated creatine kinase (CK) levels and myoglobin in urine. Complications can include acute kidney injury from rhabdomyolysis and electrolyte disturbances such as hyperkalemia.

Diagnosis relies on clinical history (exposure to venomous bites or bacterial infection, or other toxin exposure) and laboratory evidence of muscle injury. Identification of the specific myotoxin may be pursued in specialized settings, though management is largely supportive.

Management focuses on addressing the underlying cause and limiting muscle damage. For envenomation, prompt administration of appropriate antivenom and supportive care is essential. General measures include aggressive intravenous hydration to prevent renal injury, careful electrolyte management, and monitoring for rhabdomyolysis-related complications. Necrotic tissue or secondary infection may require surgical intervention. Prevention and research efforts aim to characterize myotoxins, develop targeted inhibitors, and improve antivenom therapies.