Briefs: Ahhh! Spiders!

Happy Halloween everyone. I thought I’d “celebrate” by posting about some rare but still clinically important spider bites. The two that get the most press in United States are the black widow (Latrodectus mactans) and brown recluse (Loxosceles reclusa). Fortunately, there are only approximately 500 bytes a year in the United States and deaths are very rare.

Black Widow Spiders

Black widow spiders are found in the temperate and tropical zones of the earth. They normally only bite humans in self defense. Only the female is venomous to humans – It can be identified by its black color and the red hourglass shaped mark on its abdomen

The venom causes the of norepinephrine, GABA and acetylcholine via exocytosis of synaptic vesicles. It also leads to degeneration of motor endplates which leads to denervation as well as destabilization of nerve cell membranes which causes a massive influx of calcium into the cells resulting in hypocalcemia. The initial bite produces a pin prick were burning sensation and is often unnoticed. Within hours the bite site becomes red, cyanotic, urticarial and eventually a characteristic halo shaped target lesion.

Later, generalized symptoms develop – Patients will have regional lymphadenopathy near the bite site, as well as chest, abdomen and lower back pain. The pain of a Latrodectus bite can mimic that of appendicitis! Eventually, patients may develop flexor spasms, and writhe in pain. This is bad. What’s worse is the potential for hypertension, sweating, salivation, dyspnea and increased bronchosecretions along with convulsions. Untreated patients can have symptoms for up to seven days. Many will have pain in persistent muscle weakness for weeks.

Bite victims should have ice applied to the bite wound. It is certainly a good idea to update their tetanus status. Antibiotics are not routinely recommended. Most patients have pain severe enough to require IV opiates. The relative hypocalcemia may be treated with calcium gluconate. This requires appropriate cardiac monitoring and the evidence is far from ironclad. Latrodectus specific antivenom and is available in Australia and Arizona, and is appropriate for patients in which opiates and benzodiazepines are ineffective. If possible consider administering the antivenom and to the very young, the elderly, The medically fragile and those with hypertensive and cardiac disease. Relief Will come within 1 to 2 hours after administration. Reducing is rarely indicated. Many patients who received an defendant will have flulike symptoms or a serum sickness like presentation for 1 to 3 weeks following treatment. Finally it is important to note that any symptomatic pediatric patient with a black widow bite should be admitted for observation and pain control. The ICU is appropriate for any patient with cardiac compromise or convulsions.

Brown Recluse Spiders

These brown colored spiders are 1-5cm long and have a fiddle-shaped marking on their thorax.

Brown recluse spiders are nocturnal hunters. They search for prey during the months of April through October and like to hide in small spaces like closets, attics, old blankets and shoes. Most bites occur on the extremities. More potent than the venom of rattlesnakes, the brown recluse bite leads to extensive skin necrosis. Sphingomyelinase-D causes RBC lysis. Once the cell walls are damaged and intravascular coagulation process leads to clotting abnormalities, White blood cell infiltration and eventually the the aforementioned necrotic ulcer. Fortunate patients will have a local irritating reaction, whereas the unlucky ones will have a life threatening syndrome. The bite itself is relatively painless. Within a few hours there is itching, swelling, redness and tenderness over the bite. Initially the wound may appear to be a dull blue-gray macule surrounded by a pale ring. Eventually, by the third or fourth day the base becomes a chronic with a central black eschar. Full thickness necrotic ulceration occurs by 1-2 weeks.

The above cutaneous reaction is much more common than systemic symptoms. Within 1 to 3 days after the bite patients have fever, chills, myalgias and arthralgias. Very severe cases result in DIC, hemolytic anemia, and dark urine.

Management depends on whether or not the patient has local or systemic symptoms. Heat will worsen local symptoms so use ice. A polymorphonuclear leukocyte inhibitor (dapsone) may help with overall healing. It’s use is controversial in pediatrics due to the development of methemoglobinemia. Update the patient’s tetanus status if necessary. Whatever you do do not excise the lesion early on. this will just make things worse. Once the damage is done a plastic surgeon can excise and revise. Patients with systemic symptoms may benefit from glucocorticoids as steroid treatment can slow hemolysis. Close monitoring for DIC is essential. Patients with hemolysis should have their fluid status monitor closely and one should consider alkalinizing the urine. An antivenin is being currently researched. Patients with a rapidly expanding lesion or hemolysis should be admitted. Patients with minimal symptoms and reassuring labs can be seen in 24-48 hours by their physician.