An acronym describing some of the medical signs and symptoms that are NOT part of recluse spider envenomation syndrome.
When medical people attempt to diagnose a condition, they often go through a list of potential considerations known as differential diagnoses. They start with a long list of possibilities and retain those that seem likely and eliminate those that seem unlikely. Because there are many medical conditions that look like and have been misdiagnosed as brown recluse spider bite, my colleagues (two dermatologists from Missouri who are recluse bite specialists) and I published an article in JAMA Dermatology using the acronym NOT RECLUSE, with each letter describing signs or symptoms of skin lesions or epidemiology of occurrence that are NOT likely in recluse envenomation syndrome. The paper is summarized here.
YOU SHOULD NOT USE THIS INFORMATION FOR SELF-DIAGNOSIS. THIS INFORMATION IS PROVIDED HERE FOR YOU TO PRINT OUT AND TAKE TO THE DOCTOR WHO IS TREATING YOU TO HELP DETERMINE IF A BROWN RECLUSE BITE IS LIKELY OR NOT.
Stoecker, W. V., R. S. Vetter and J. A. Dyer. 2017. NOT RECLUSE – a mnemonic device to avoid false diagnosis of brown recluse spider bites. JAMA Dermatology 153: 377-378.
N - numerous: Most recluse bites (and spider bites in general) are singular wounds where the spider will bite when being near fatality crushed between skin and some other surface. If there are multiple lesions, consider bacterial infections, shingles, pyoderma gangrenosum, bites by blood-feeding arthropods (fleas, mites, bedbugs), poison ivy, poison oak.
O - occurrence: Many bites occur when a sleeping person rolls over on a spider in bed or when dressing in the morning, putting on shoes or clothes that sat out on the floor overnight. Also, bites may occur when disturbing possessions in the attic, garage or basement. Recluses do not live in green vegetation so skin lesions that show up after gardening might be a plant-related fungal infection called sporotrichosis especially if lesions show up on the forearms and backs of the hands.
T - timing: Most recluse bites occur from April to September in the Northern hemisphere. Even in heated homes, recluses disappear for the winter. Skin lesions appearing during October to March "down time" are unlikely to be recluse bites. Exception: recluses might be disturbed when unpacking year-end holiday decorations taken out of storage.
R - red center: Except for mild envenomations, recluse bites are not red in the center of the lesion. Recluse venom destroys the capillary network at the bite site so red blood cells can't get to the area. The more dynamic bites will be white, blue or purple at the bite site. If there is a red center, the differential diagnoses include streptococcal cellulitis or an arthropod bite or sting.
E - elevated: Recluse bites are flat or slightly sunken. If a lesion is raised up more than 1 cm above the normal skin surface, recluse bite is unlikely. Differential diagnoses include bacterial infection such as MRSA (methicillin-resistant Staphylococcus aureus).
C - chronic: Most recluse bites are healed by the third month. Differential diagnoses for longer lasting lesions include: pyoderma gangrenosum, non-melanoma skin cancer, tularemia.
L - large: Most recluse bites do not become larger than 10 cm (2 1/2 inches). Larger lesions might be pyoderma gangrenosum.
U - ulcerates too early: Recluse envenomations don't usually ulcerate until day 7 to day 14. Earlier ulceration might be pyoderma gangrenosum or the very rare anthrax infection.
S - swelling: Recluse bites typically do not involve much swelling below the neck or above the ankles. However, bites above the neck can involve significant swelling, which can compromise breathing passages. Major swelling from below the neck to ankles indicates streptococcal cellulitis, bacterial infection or bee/wasp/ant bite/sting.
E - exudative: This may be the most important sign indicating that it is not a recluse bite: exudative. Recluse bites may form a small fluid-filled blister at the bite site soon after the bite but, in general, recluse bites are usually dry. If a skin lesion is exuding pus, blood or serum that indicates something other than spiders is the cause. One of the most common conditions mistaken for spider bite by the general public is a bacterial infection. The resistant MRSA is very common in human populations worldwide. A deep, weeping wound, especially on the lower leg might be pyoderma gangrenosum.