A 29-year-old female presented to the emergency department for a rash on her right calf. 5 days prior, at her home in Alabama, the patient developed pain and swelling of her right calf following a spider bite while putting on her pants. The patient felt a “burning pain” and found a spider which she then killed. She went to a hospital and received cephalexin, trimethoprim/sulfamethoxazole, and oxycodone. Despite taking these medications she continued having aching pain rated 10/10 in her right calf along with generalized pruritus. The patient stated that the bite evolved from an initial generalized redness into a blue/black lesion with blistering and extensive redness along her leg and torso. She denied fever, chills, lightheadedness, abdominal pain, nausea, vomiting, and hematuria.

Vitals: BP 126/67; HR 108; Temp 98.1 degrees F; RR 16; O2 sat 98% on room air

Musculoskeletal: Swelling to right calf, tender to palpation, soft compartments

Skin: Right lower extremity with erythema extending from the calf into the right groin, abdomen, and chest. On the right calf, there is a 10 cm x 10 cm region of ecchymosis with scattered hemorrhagic bullae.


  • Leukocyte esterase: none
  • Nitrites: none
  • Blood: moderate
  • WBC: 3
  • RBC: 64
  • Bacteria: none
  • Squamous cells: 5

Brown recluse spider (Loxoscelese reclusa) bite

There are multiple conditions that may mimic loxoscelism, such as cellulitis, localized vasculitis, pyoderma gangrenosum, and gonoccocemia, amongst many others. Therefore, a diagnosis requires sound clinical judgment along with a strong history of brown recluse bite. The particular factors most supporting the diagnosis in this patient include her residence in Alabama and progressive dermatologic changes.

Geography is key to a diagnosis of loxosceles envenomation since brown recluse spiders are endemic in central and southern states. Outside of these endemic regions within the continental United States (US), physicians should be cautious about diagnosing loxosceles envenomation [1].

The bites typically present as a plaque of erythema with central pallor, sometimes with surrounding vesiculation that is self-limited. The bites can become necrotic with an overlying eschar, as seen here, and patients should be informed early in the course of their presentation that bites are at high risk for necrosis.

Systemic loxoscelism

Systemic loxoscelism can develop 24 to 72 hours after a bite, resulting in hemolysis, rhabdomyolysis, and even disseminated intravascular coagulation (DIC). Pediatric patients are most susceptible to systemic loxoscelism, and urinalysis is a useful screening lab that can identify hemolysis early in the course of a systemic reaction. Given hematuria on urinalysis and severe pain, this patient was admitted for further observation and care.

Her fibrinogen level, haptoglobin, and lactic acid dehydrogenase (LDH) were all within normal limits and hemoglobin/hematocrit remained stable over her hospital course. Based on these collective findings, the hematuria was hypothesized to have been a contaminant from her current menstrual cycle. Nonetheless, systemic loxoscelism can be a true emergency requiring multiple transfusions and carries a high risk of death if not promptly recognized or respected.

The ultimate clinical care of brown recluse bites includes ice, elevation of the affected limb (if practical), and tetanus vaccine booster. A myriad of additional therapies, such as dapsone, have been proposed as treatment modalities. No randomized control trials, however, have demonstrated their efficacy or improved patient outcomes.

Take-Home Points

  • No single study confirms the diagnosis of a brown recluse bite, and both history and dermatologic findings are essential for a diagnosis.
  • Necrosis is a common complication of brown recluse bites and patients should be informed early on regarding the potential clinical course of a bite.
  • Systemic loxoscelism with resulting hemolytic anemia is a life-threatening complication associated with brown recluse bites that can be screened for with a urinalysis. A urine dip positive for blood without significant RBCs is suggestive of hemolysis and should prompt further lab testing [2].
  1. Swanson DL, Vetter RS. Bites of brown recluse spiders and suspected necrotic arachnidism. New Engl J Med. 2005;352 (7):700. PMID: 15716564
  2. Murray L, Seger D. Hemolytic anemia following presumptive brown recluse spider bite. J Toxicology: Clinical Toxicology. 1994;32(4):451–56. PMID: 8057405

Andrew D’Alessandro, MD

Andrew D’Alessandro, MD

Vanderbilt University Medical Center
Andrew D’Alessandro, MD

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Elena James, MD

Elena James, MD

Vanderbilt University Medical Center
Elena James, MD

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