In-Service Exam
Soft Tissue Infection - 2001





Which of the following best characterizes black widow spider (Latrodectus mactans) venom?

(A) Hemotoxin
(B) Myelotoxin
(C) Neurotoxin
(D) Tissue toxin

The correct response is Option C.

The venom of the black widow spider (Latrodectus mactans) is a neurotoxic agent that causes the hallmark findings of muscle pain and cramping that appear within 15 minutes after the bite. This common species of spider is found throughout the United States. Most patients with latrodectism are bitten by female spiders; in contrast, the bite of the male spider rarely penetrates the skin. Affected patients have sharp pain at the wound site with two small red spots marking the location of puncture. Late findings include pain and cramping of the striated muscles, abdominal pain, vomiting, tremor, excessive salivation, and shock.

In a patient who is bitten by a black widow spider, the most appropriate therapy is administration of 10 mL of 10% calcium gluconate solution over a period of 15 to 20 minutes; 1 ampule of methocarbamol or 5 mg to 10 mg of diazepam can be administered additionally. Improvement of the patient's symptoms following treatment is diagnostic of latrodectism. In immunocompromised patients, a diluted dose of black widow spider antivenin (Lyovac) should be administered intravenously at a slow rate.

In contrast, the brown recluse spider produces a toxin known as sphingomyelinate, a dermonecrotic factor. Envenomation with sphingomyelinate results in hemolysis, coagulation, and platelet aggregation, often affecting fatty tissue. Symptoms can range from mild irritation to severe necrosis.

Hemotoxins, such as cobra venom, are exotoxins that result in hemolysis.

References
1. Blackman JR. Spider bites. J Am Board Fam Pract. 1995;8:288-294.
2. Koh WL. When to worry about spider bites: inaccurate diagnosis can have serious, even fatal, consequences. Postgrad Med. 1998;103:235-236, 243-244, 249-250.
3. Wallace JF. Disorders caused by venoms, bites, and stings. In: Isselbacher KJ, Braunwald E, Wilson JD, et al, eds. Harrison's Principals of Internal Medicine. 13th ed. New York, NY: McGraw-Hill, Inc; 1994;2:2467-2473.

A patient develops an infection at the wound site five days after beginning leech therapy. Which of the following is the most appropriate antibiotic therapy?

(A) Cephalexin
(B) Clindamycin
(C) Metronidazole
(D) Penicillin
(E) Trimethoprim-sulfamethoxazole

The correct response is Option E.

This patient has developed infection with Aeromonas hydrophila after undergoing leech therapy for five days. Medicinal leeches such as the Hirudo medicinalis species (which is the most commonly used leech and is endemic to Southeast Asia and Europe) can be applied to flaps or replanted limbs in order to relieve venous congestion. However, a common complication of leech therapy is the development of infectious organisms such as Aeromonas hydrophila, a gram-negative rod that can be detected in as many as 20% of persons within the first 10 days of therapy. Infiltration of Aeromonas hydrophila organisms can result in a rapidly progressive infection with gas in the soft tissues that can resemble clostridial myonecrosis. If infection does develop, trimethoprim-sulfamethoxazole is recommended for first-line therapy. Fluoroquinolones such as ciprofloxacin are also effective. Antibiotics that are still effective but less frequently recommended include antipseudomonal aminoglycoside, imipenem, meropenem, tetracycline, and second-, third-, or fourth-generation cephalosporins.

References
1. Gilbert DN, Moellering RC, Sande MA. The Sandford Guide to Antimicrobial Therapy. 29th ed. Antimicrobial Therapy, Inc; 1999.
2. Gross MP, Apesos J. The use of leeches for treatment of venous congestion of the nipple following breast surgery. Aesthet Plast Surg. 1992;16:343.
3. Lineaweaver WC, Hill MK, Buncke GM, et al. Aeromonas hydrophila infections following use of medicinal leeches in replantation and flap surgery. Ann Plast Surg. 1992;29:238.
4. Siftan D, ed. Physician's Desk Reference. 54th ed. Montvale, NJ: Medical Economics Corp; 2000.

PHOTO

A 34-year-old man is brought to the emergency department after sustaining a snake bite to the dominant right thumb. A photograph is shown above. The patient has severe pain, nausea, and vomiting. On examination, the distal forearm is tense. Prothrombin time and partial thromboplastin time are increased. The snake has been captured and was brought to the emergency department by the patient; a photograph is shown above.

Which of the following is the most appropriate management?

(A) Elevation of the extremity, application of ice, and intravenous administration of antibiotics
(B) Elevation of the extremity, application of ice, intravenous administration of antibiotics, and administration of antivenin
(C) Incision and suction drainage of the bite wound, elevation of the extremity, application of ice, and intravenous administration of antibiotics
(D) Fasciotomy and intravenous administration of antibiotics
(E) Fasciotomy, intravenous administration of antibiotics, and administration of antivenin

PHOTO

The correct response is Option E.

This patient who has sustained a pit viper bite to the dominant right thumb requires immediate treatment involving fasciotomy, intravenous administration of antibiotics, and administration of pit viper antivenin. Approximately 98% of venomous snake bites are from pit vipers, and more than 70% of these bites involve the upper extremity. Pit vipers can be distinguished from other snakes by the presence of two retractable maxillae, each of which contains a fang for envenomation. In patients who sustain pit viper bites, immediate first aid should consist of patient reassurance, immobilization of the affected limb and placement of the limb on a level plane, and transportation to a hospital as soon as possible. Envenomation should be assumed with the presence of fang marks and rapid swelling of the extremity; broad-spectrum antibiotics should be administered immediately in the emergency department. Patients who have tense edema of the affected extremity and compartment pressures of greater than 30 mmHg should be diagnosed with compartment syndrome. Urgent fasciotomy should be performed.

Because snake venom can greatly worsen myonecrosis and systemic findings, antivenin should be administered to any patient who has systemic symptoms of envenomation associated with increased laboratory values. Following administration of a test dose, five to 10 vials of snake antivenin are typically administered in patients who do not exhibit allergic sensitivity. A central line should be placed and emergency resuscitation should be available. The administration of as many as 20 vials of antivenin may be required in patients who have extreme abnormalities on laboratory evaluation.

Application of ice will result in vasoconstriction, ischemia, and tissue necrosis. Incision and suction drainage of the bite wound should be performed within 15 minutes of the bite.

References
1. Carels RA, Janse M, Klaver PS, et al. Acute management of patients bitten by poisonous snakes. Ned Tijdschr Geneeskd. 1998;142:2773-2777.
2. Cowin DJ, Wright T, Cowin JA. Long-term complications of snake bites to the upper extremity. J South Orthop Assoc. 1998;7:205-211.
3. Mattison C. The Encyclopedia of Snakes. United Kingdom: Blanford; 1995.
4. Norris RL Jr. Envenomations. In: Intensive Medicine. Boston, Mass: Little, Brown & Co; 1996:1585-1590.
5. Rowland SA. Fasciotomy: the treatment of compartment syndrome. In: Green DP, Hotchkiss RN, Pederson WC, eds. Operative Hand Surgery. 4th ed. New York, NY: Churchill Livingstone, Inc; 1999;1:689-710.

Over the past nine months, a 58-year-old woman has had four episodes of paronychia of the right middle finger characterized by pain, swelling, and inflammation. She has taken oral antibiotics intermittently during that time; there is no purulent drainage.

Which of the following is the most likely causal organism?

(A) Candida albicans
(B) Herpes simplex virus
(C) Mycobacterium marinum
(D) Pseudomonas aeruginosa
(E) Staphylococcus aureus

The correct response is Option A.

In this patient who has a history of recurrent inflammation consistent with chronic paronychial infection, the most likely causal organism is Candida albicans, which has been shown to be responsible for as many as 97% of cases of chronic paronychia. In patients with this condition, the affected area should be kept dry and a topical antifungal agent such as clotrimazole should be applied. Eponychial marsupialization, which involves the removal of a crescent-shaped piece of skin from the eponychium, may be considered to clear the scarred, infected tissues.

Herpes simplex virus results in herpetic whitlow, an extremely painful condition characterized by visible vesicles. It is self-limiting and typically resolves in three to four weeks, but may recur. Incision and drainage are not indicated.

Mycobacterium marinum, an atypical mycobacterium, can result in superficial or deep granulomatous infections. The recommended treatment includes multidrug antituberculous therapy and surgical debulking.

Although Pseudomonas aeruginosa is part of the normal flora of the hyponychial space, this organism can result in acute infection in patients with diabetes mellitus or can be a secondary cause of chronic paronychia. Discoloration of the nail is a frequent finding.

Staphylococcus aureus is the predominant pathogen associated with acute paronychial infection, which manifests as an abscess requiring incision and drainage.

References
1. Floyd WE, Troum S, Frankle MA. Acute and chronic sepsis. In: Peimer CA, ed. Surgery of the Hand and Upper Extremity. New York, NY: McGraw-Hill, Inc; 1996;2:1731-1762.
2. Jebson PJ. Infections of the fingertip. Hand Clin. 1998;14:547-555.
3. Patel MR. Chronic infections. In: Green DP, Hotchkiss RN, Pederson WC, eds. Operative Hand Surgery. 4th ed. New York, NY: Churchill Livingstone, Inc; 1999;2:1783-1850.