The accurate diagnosis and treatment of tegenarism
(hobo spider poisoning) presents a relatively new challenge to physicians and
other health care workers in the northwestern
Spider bites are placed into three separate categories; possible, probable,
and proven. Possible spider bite applies to those cases in which the
physician feels could be a bite by a spider, but which lack sufficient
clinical or circumstantial evidence to support a firm diagnosis. Probable
spider bite applies to those cases in which the clinical and/or circumstantial
evidence support the likelihood of spider bite, but the biting spider was not
recovered and positively identified. Proven spider bite applies to those
cases in which the clinical and circumstantial evidence support the diagnosis
of spider bite, and the biting spider was captured and positively
identified. Approximately 80% of suspected spider bites seen in
Upon admission to the clinic or emergency room, the first diagnostic consideration (when presented with possible or probable spider bites) should be to rule out or confirm other possible causes. Delayed type hypersensitivity (DTH) and immediate type hypersensitivity (ITH) reactions to the bites of parasitic arthropods are the lesions most commonly mistaken for "spider bite". These two types of reactions may closely resemble the very early stages of necrotic spider bite lesions (the DTH reaction may occasionally exhibit very limited centralized necrosis), but neither will produce deep, persistent dermal necrosis. Suspect "spider bites" that appear in rows or patches are almost always bites by parasitic arthropods, which often bite and feed at one site, then move a centimeter or two and bite again. Spider bites are usually single, unless the biting spider was caught between tissue and clothing and could not escape.
Mycoinfections, particularly tinea
corporis, are another common differential diagnosis
of spider bite in the northwestern
Viral infections with cutaneous manifestations may
also be considered a differential diagnosis for suspected spider bite. Herpes
zoster has been the actual causative agent in a number of suspected
"spider bite" cases in the
In proven cases, where the patient actually brings the biting spider
(or its remains) to the clinic, it is important to seek a positive
identification of the specimen at once. While a tentative identification
can be made at the clinic, positive identification, as well as age and sex
determination by a qualified arachnologist is
important; all of these factors can effect the
severity and course of a hobo spider envenomation. In
Spiders submitted for positive identification should always be accompanied with basic collection information, including the date, the exact location (street address, etc.), the name of the collector(s) and any other information about the spider that is available. Questions directed to Rod Crawford should concern spiders and/or spider identification, not questions regarding bites or envenomation.
Once the diagnosis of proven or probable hobo spider bite is established, a determination can be made as to the severity of the case, and treatment protocols can be implemented. Most patients will present exhibiting local effects only, and can be treated as outpatients. Tetanus prophylaxis is indicated, and the patient should be advised to clean the wound frequently, and (if on an extremity) to keep it immobilized and rested. Diphenhydramine (Benadryl) may be prescribed to help control itching. Prophylactic antibiotic therapy is not warranted, and antibiotics should be used as needed only to control secondary infection. Laboratory studies, including a CBC with platelets, Hb, Hct, BUN, creatinine and urinalysis are advisable in all cases of tegenarism. The patient should be scheduled with a followup visit, and should be told to watch the lesion closely for signs of darkening, etc. It is good practice to inform the patient of the typical healing time-table (see Hobo Spider Poisoning): It is also good to inform the patient (at each visit) that lesions of necrotic spider bite are often difficult to predict, and can sometimes get progressively worse.
Subjects that are bitten in areas which contain large amounts of adipose tissue, particularly if the victim is obese, are at high risk for the development of deep, slow healing lesions. In such cases excisional therapy is not indicated, and may exacerbate the condition of the lesion. While natural healing by slow granulation is preferred, split thickness skin grafts may be considered after the necrotizing process is completed (8 weeks); The initial graft attempt is usually not successful.
Patients exhibiting systemic effects of tegenarism should have the above mentioned laboratory screen performed immediately. If evidence of any significant abnormalities (except a moderate leukocytosis) are discovered, the patient should be given a regimen of a prednisolone based corticosteroid, and should be hospitalized. Typically, a tapered dose starting with the equivalent of 4 mg of Decadron is recommended. Some physicians experienced with tegenarism prefer to administer corticosteroids whether or not systemic effects are present; considering the insidious nature of some effects of hobo spider poisoning, this practice may have merit. Antianxiety medications such as hydroxyzine (Atarax) have proven beneficial to systemically poisoned hobo spider bite victims, and may provide some comfort to nervous or emotionally upset victims of any necrotic spider bite.
Tegenarism is a relatively new disease state and
much is yet to be learned from it. An excellent clinical reference on necrotic arachnidism (published largely on the bite of the brown
recluse spider, before the hobo entered the scene), is Wasserman,
G.S. and Anderson, P.C. (1983-84): Loxoscelism and
necrotic arachnidism. J. Toxocol.-Clin.
21(4 &5), pp. 451-472. Physicians that have treated hobo
spider bite cases are encouraged to publish case histories and observations on
back to the Hobo Spider Web Site
Go to Books on Bites/Stings, Venoms/Venomous Organisms
©1999 Darwin K. Vest, Eagle Rock Research