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Spiders: Differential Diagnosis

Latrodectus

The main difficulty in diagnosing black widow spider envenomation is that the spider is rarely captured and brought in for definitive identification. Furthermore, if the history of the spider bite and the clinical syndrome of envenomation are not recognized, the differential diagnosis can be quite broad. The malaise, muscular discomfort, and lymphadenopathy can be initially misdiagnosed as a flulike syndrome. The muscle cramping and facial grimacing can be interpreted as seizures. Patients can also develop dysautonomia with nausea, vomiting, malaise, sweating, tachycardia, and dysphoria which can all be misdiagnosed as sepsis, acute gastroenteritis, dehydration, nicotinic toxicity, or food poisoning. The pain from a Latrodectus bite is so excruciating that it can be mistaken for myocardial infarction or acute abdomen, particularly when the original spider bite was not observed. Other conditions, such as muscle strain, meningitis, cocaine intoxication, and psychosis, may also be considered.29,33

Loxosceles

The diagnosis of brown recluse spider envenomation can be difficult if the spider is not positively identified or if the envenomation is not suspected after either the history or physical examination are obtained. The clinician may have a tendency to assume any dermatonecrotic lesion is a brown recluse spider envenomation. Other etiologic possibilities include bacterial infection, fungal infection, pyoderma gangrenosum, viruses, adverse drug reactions, other arthropod bites, thromboembolic phenomenon, Lyme disease, neoplasms, chemical burns, and necrotizing fasciitis. The differential diagnosis for systemic loxoscelism includes Toxic Shock Syndrome, sepsis with disseminated intravascular coagulation, hemolytic uremic syndrome, and other causes of extensive hemolysis. Also, airway compromise may occur if the patient develops significant airway swelling in reaction to the bite.32,36,59,60

Making the correct initial diagnosis is important and requires the diagnostician to take a careful history and be aware of the typical presentation of Loxosceles envenomation, including dermatonecrosis and systemic toxicity.


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Last Modified: 08/17/2017
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