A 30 year‐old man presented with a one‐day history of a sudden painful rash on his left arm that began while sitting on a bench in his yard. Four hours after the rash appeared he felt a burning sensation in his arm. Twelve hours later, he experienced chest tightness, shortness of breath, knee pain, muscle spasms, blurred vision, and agitation. He had a target‐like rash with a central, indurated 1 cm bite mark in the center of a 6 cm erythematous circular lesion. The area was tender, swollen and warm to touch. The patient’s abdomen was diffusely tender, and aside from the arm lesion, the remainder of the physical examination was unremarkable. Six hours after presentation the circular lesion expanded to 16‐cm. His agitation increased and he continued to complain of chest tightness. His CBC, CMP, UA, and EKG were normal. CK was 105. On admission, his blood pressure was 123/97 mmHg, heart rate 85 bpm, respiratory rate 32, and he had a normal temperature.
On further questioning he produced a jar with a brown widow spider, which he collected from the porch area shortly after being bitten. He was treated with intravenous clindamycin 450mg q6 hours, intravenous methylprednisolone 125mg, benzodiazepines, anti‐histamines, opiate analgesics, and a tDAP booster. Within 12 hours, his rash improved to 6 cm, and his symptoms resolved. He was discharged on oral clindamycin.
Cellulitis is commonly encountered by hospitalists and, in the southeastern United States, many of these episodes result from reported insect bites, often “spider bites”. If the spider species can be identified, a predictable clinical course may be identified based on envenomation patterns. Brown widow (Latrodectus geometricus) bites are especially concerning because the venom contains a vertebrate‐specific neurotoxin, α‐latrotoxin, that releases neurotransmitters, such as acetylcholine and norepinephrine from presynaptic nerve terminals. The resulting cholinergic and adrenergic events can anticipate the progression of the patient’s symptoms.
Lactrodectism, a bite by a Lactrodectus spider, may result in mild envenomation. This consists of local skin irritation associated with muscle pain and spasms adjacent to the bite. Treatment at this stage consists of local wound care, analgesia and tetanus prophylaxis. With moderate envenomation, patients exhibit spasmodic muscle pain in the bitten extremity, which can generalize to the back, chest, or abdomen, and can be accompanied by diaphoresis. This is treated supportively as with mild envenomation. Severe cases can present with pain that is difficult to control and can be accompanied by vital sign instability such as tachycardia and hypertension, as well as systemic signs such as nausea, vomiting, and headache. These cases may require antivenin. A toxicology consult is helpful in determining the appropriate course of action; if a local consult in unavailable, state toxicologist can be contacted by phone. Although antivenin is associated with shorter symptom duration, adverse drug reactions such as anaphylaxis, limit this intervention. Only one death has been reported due to latrodectism and was secondary to cardiac arrest.
Hospitalists may encounter insect bites as a source for cellulitis. Recognition of the type of insect involved can lead to appopriate treatment in a timely fashion.