Thursday, July 31, 2014

Scorpion Envenomation. Not so bad, but when it bad... is BAD!

Still is summer time and in some parts of the world, scorpions are a threat. There are dozens of varieties to chose from. Here are some basics about the patophysiology of Scorpion Envenomation. From this week's NEJM.

What are the general characteristics of scorpion stings?
Most scorpion stings cause localized pain, whereas only an estimated 10% of stings, even from the most dangerous scorpions, result in severe systemic envenomation. Edema, erythema, paresthesias, muscle fasciculations, and numbness may occur at the site of the sting. It is often difficult to see the sting site or to identify inflammation at the site, despite substantial local pain. Most cases of severe envenomation occur in children. Systemic envenomation is characterized by neuromuscular abnormalities resulting from effects on the somatic and cranial nerves, both cholinergic and adrenergic excitation of the autonomic nervous system, pulmonary edema, and cardiac effects.
What are the autonomic effects of scorpion stings?
Excitation of the autonomic nervous system is characterized by both parasympathetic and sympathetic responses. Parasympathetic, cholinergic effects may include hypersalivation, profuse diaphoresis, lacrimation, miosis, diarrhea, vomiting, bradycardia, hypotension, increased respiratory secretions, and priapism. Sympathetic, adrenergic effects include tachycardia, hypertension, mydriasis, hyperthermia, hyperglycemia, agitation, and restlessness. Whereas most parasympathetic effects tend to occur early, sympathetic effects persist because of the release of catecholamines and are responsible for severe envenomation.
What are possible cardiovascular complications of scorpion envenomation? A range of cardiac conduction abnormalities occur in about one third to one half of patients with systemic envenomation. These effects include atrial tachycardia, ventricular extrasystoles, T-wave inversion, ST-T wave changes, and, less frequently, bundle-branch block. Increased autonomic stimulation caused by increased vagal effects on the heart and sympathetic stimulation are the probable causes of these effects. Hypertension is common and occurs early in response to sympathetic stimulation. Hypotension is less common, occurs with the development of severe envenomation, and often requires intervention with vasopressors and fluid resuscitation. Many factors are at play in the development of hypotension, with cholinergic stimulation causing vasodilation, fluid loss, and myocardial depression. Cardiac dysfunction resulting from catecholamine-induced myocarditis and myocardial ischemia complicates severe envenomation from androctonus, buthus, mesobuthus, and tityus scorpions. This complication may result in pulmonary edema and cardiogenic shock.

What are the principles of treatment for cases of severe scorpion envenomation? The specific treatment is the administration of antivenom combined with symptomatic and supportive treatment, including prazosin and dobutamine in patients with cardiovascular toxic effects and benzodiazepines when there is neuromuscular involvement. Symptoms related to the site of the sting should be managed with appropriate analgesia with acetaminophen and antiinflammatory agents, depending on severity. Once severe envenomation has developed, the administration of antivenom may be less effective, since its primary therapeutic action is to bind toxins; it does not reverse established pathophysiological injury, such as excess levels of catecholamine, pulmonary edema, and cardiogenic shock.
- Scorpion envenomation are rarely fatal, but children are at high risk.
- For most, supportive treatment is fine if no signs of nervous or cardiac system involvement. 
- If is going to be bad, it goes from bad to worse very quickly. Therefore, if antivenom is available, give it early and transfer sooner rather than later.
- Prazosin, an alfa blocker, and dobutamine in combination for patients with cardiovascular symptoms. And benzos for neuromuscular involvement.
- Not all scorpions are scary, some can also be cute... like this one!