A patient bitten by the pictured creature with the pictured lesion should be screened for which pathology?

  1. Acute liver failure
  2. Ascending paralysis
  3. Hemolysis
  4. Meningitis
  5. Myocarditis

Answer: C – Hemolysis

Brown Recluse Spider Bite (1,2,3)

  • The Loxosceles reclusa, or brown recluse spider, is one of several under the Loxosceles genus whose bites may produce dermatonecrotic wounds and rarely systemic effects such as hemolysis.
  • The cytotoxic enzyme Sphingomyelinase D is believed to be primarily responsible for the dermatonecrotic effects
  • Brown recluse spiders are found worldwide, and within the United States are limited to certain geographical areas, mostly in the southern states.
  • Definitive epidemiological data are lacking, as with many cases of suspected envenomation, there is no spider found for confirmation.
  • Brown recluse spiders commonly make their homes in household areas like attics or basements, and while they are not known to be aggressive, they will bite if threatened.
  • In the United States, recluse bites tend to peak between March and October.
  • While physical attributes are not entirely reliable in distinguishing the brown recluse from other harmless spiders, they are distinct in having six eyes, as opposed to eight, arranged in three dyads. They also have a characteristic fiddle shape on the dorsal thorax.
  • Typically they are not found outside of endemic areas therefore clinicians should maintain a high degree of skepticism if the patient has not been to an endemic area.
  • The differential diagnosis for a dermatonecrotic lesion is broad and includes numerous treatable conditions.

Clinical manifestations (1,4,5)

  • A painless bite followed by increased local pain over hours.
  • Over 1-3 days, some patients develop a variegated rash/lesion surrounding the bite referred to as “red, white, and blue” representing “erythema, ischemia, and thrombosis.”
  • Over the next few weeks, the bites have a variable course, but often form an eschar that will fall off on its own.
  • Fever and diffuse erythematous rash that occurs over the first 1-3 days from the bite suggests systemic envenomation known as loxoscelism.
  • Systemic loxoscelism can induce rapid hemolysis (cutaneous-hemolytic loxoscelism), acute renal failure, rhabdomyolysis, or disseminated intravascular coagulation (DIC).
  • Hemolysis can be intravascular or extravascular and is thought to be related to the actions of sphingomyelinase on the red blood cell membrane.

Management (1,6,7)

  • Management of the bite is supportive with wound care, oral analgesia, and ice appearing to be highly effective for pain control.
  • The bite should be left open to air unless ruptured bullae are present
  • Steroids and other topical treatments should be avoided.
  • Surgical intervention is not routinely indicated.
  • Patients with fever or diffuse rash and the suspected recluse bite should be screened for hemolysis with a urinalysis and complete blood count (CBC).
  • Urinalysis positive for blood without red blood cells on microscopy should prompt concern for ongoing hemolysis.
  • Admit patients with cutaneous hemolytic loxocelism or superinfected or concerning lesions such as those on the face.
  • Treatment for hemolysis is supportive with transfusion of blood products as indicated.
  • Loxosceles antivenom exists but is currently unavailable in the United States.

Bedside Pearls

  • Maintain a broad differential for patients with dermatonecrotic lesions presenting outside of endemic areas or when a spider is not identified.
  • Be aware of the “red, white, and blue” rash in areas where recluse spiders are endemic.
  • Fever and/or diffuse rash after presumed bite suggests systemic loxoscelism and these patients warrant screening for hemolysis with a urinalysis and CBC.
  • Supportive treatment is the mainstay of therapy in the United States


Donna Seger, MD. Executive Director, Tennessee Poison Center.


The pictured lesion is from a patient diagnosed by medical toxicology consultation with a presumed brown recluse spider bite based on clinical presentation and course, however, no spider was identified.

This post has been peer-reviewed on behalf of ACMT by Brent Furbee, Bryan Judge, and Louise Kao


      1. Repplinger DJ, Hahn I. Arthropods. In: Nelson LS, Howland M, Lewin NA, Smith SW, Goldfrank LR, Hoffman RS. eds. Goldfrank’s Toxicologic Emergencies, 11e. 2019 McGraw-Hill.
      2. Vetter RS. Arachnids submitted as suspected brown recluse spiders (Araneae: Sicariidae): Loxosceles spiders are virtually restricted to their known distributions but are perceived to exist throughout the United States. Journal of Medical Entomology. 2005;42(4): 512–521. PMID: 16119538
      3. Kurpiewski G, et al. Platelet aggregation and sphingomyelinase D activity of a purified toxin from the venom of Loxosceles reclusaBiochim Biophys Acta. 1981;678:467–476. PMID: 6274420
      4. Sams HH, Dunnick CA, Smith ML, King LE. Necrotic arachnidism. Journal of the American Academy of Dermatology. 2001;44(4):561-576. PMID: 11260528
      5. Loden JK, Seger DL, Spiller HA, Wang L, Byrne DW. Cutaneous-hemolytic loxoscelism following brown recluse spider envenomation: new understandings. Clin Toxicol (Phila). 2020 Mar 18:1-9. doi: 10.1080/15563650.2020.1739701. PMID: 32186919
      6. Rosen JL, Dumitru JK, Langley EW, Meade Olivier CA. Emergency department death from systemic loxoscelism. Ann Emerg Med. 2012 Oct;60(4):439-41. doi: 10.1016/j.annemergmed.2011.12.011. PMID: 22305333
      7. Lindsay M. Murray & Donna L Seger (1994) Hemolytic Anemia Following a Presumptive Brown Recluse Spider Bite, Journal of Toxicology: Clinical Toxicology, 32:4, 451-456. PMID: 8057405
Michael Simpson, MD

Michael Simpson, MD

Emergency Medicine Resident
Vanderbilt University Medical Center
Michael Simpson, MD

Latest posts by Michael Simpson, MD (see all)

Rebecca Bruccoleri, MD

Rebecca Bruccoleri, MD

Medical Toxicology Faculty
Vanderbilt University Medical Center
Rebecca Bruccoleri, MD

Latest posts by Rebecca Bruccoleri, MD (see all)