Horse bite injury

ARTICLE

Bite wounds in humans are fairly commonly observed, being in order of frequency: dogs, cats and humans [1]. Snake bites are interesting mainly from the point of view of their poisonous effects. Other animal bites are reported because of the danger of serious infection: rabies in foxes, coyotes, skunks, bobcats, raccoons and bats [2]. Some monkeys of the Old World can cause infection with Simian Herpes B Virus [3], and pet hamsters have been implicated in outbreaks of lymphocytic choriomeningitis [4]. Rodents such as pet rats, can transmit rat bite fever, resulting from infection with Streptobacillus moniliformis [5]. Dogs, cats, and farm animals such as horses and sheep can transmit Pasteurella multocida [6, 7] and Actinobacillus sp [8-10] because of their presence as oropharyngeal flora. Despite this, horse bites are very rarely reported in the medical literature.

Recent reports on skin imaging have increased the interest in ultrasonography (US). Exploring the muscle, aponeurosis and fat with the 5-7.5-10 MHz transducers, or just the skin with the 12, or better the new 20 MHz US scanner, is now feasible [11, 12].

Case report

In September 1996, we saw a 37 year-old Caucasian woman in the outpatient clinic who presented with a banal, dermatological condition (epidermal cyst exeresis).

She also complained of left thigh pain related to a horse bite which she had received 24 hours earlier.

On physical examination we observed, on the external aspect of the medium third of the left thigh, a 10 cm diameter ecchymosis over an area of tumefaction. The thigh was warm, swollen and tender, with superficial linear erosions caused by the horse's teeth. There was also partial limitation of mobility. Careful palpation revealed deep fluctuation, so we decided upon excision. Under sterile conditions, about 125 ml of dark blood, with the remains of fat lobules were drained, and then the area was irrigated with normal saline solution. A Jackson-Pratt drainage was put in place, and the thigh was wrapped in a light compressive dressing.

Absolute rest for three days was recommended, and antitetanus immunization, Cloxacyllin 500 mg q.i.d., dexketoprofen trometamol b.i.d., and benzodiazepine were prescribed. One week later, the lesion was reexamined. There was a large ecchymosis, wider than when first seen, and superficial linear erosions due to the horse's teeth in addition to the surgical incision to facilitate drainage (Fig. 1). The thigh was still tender, and movement remained painful.

At that time, we performed a soft tissue ultrasonography, with a standard 5-7.5 MHz transducer equipment in order to exclude deeper damage. An intramuscular mass, measuring 5 x 5 x 15 mm, in the postero-external aspect of the left thigh, possibly related to muscle haematoma as a result of bunch rupture (Fig. 2). The subcutaneous tissue showed no lesion. Two weeks later (D+30), when we repeated the ultrasonography, there was no sign of the muscular lesion.

One year after the injury, the area remained slightly depressed, with hypoesthesia, hypohidrosis and decreased vellus hair, all probably related to trophic and cicatricial changes. A recent, standard ultrasound examination showed no gross changes in the thigh muscle or fat.

Discussion

Usually horses produce wounds on the hands, or upper limbs [6-7], although other areas such as the face [8] or thigh, can be involved. A personal communication with the Medical Officer of the "Guardia Real" ­ Spanish Royal Guard ­ confirmed that horse bites are very frequent among stablemen from the Lancers' Squadron. They affect mostly forearms, arms and neck, and sometimes the ears or back, and usually occur when the horse is feeding. The wounds are superficial, with ecchymoses of variable intensity, due to the blunt incisors, so seldom need hospital care.

As far as we know, this is the first reported case of an extensive, deep lesion without an external wound (crush injury) caused by a horse bite. It is interesting to note the need for a rapid surgical procedure with drainage of blood and necrosed fat in order to avoid necrosis and/or gangrene.

The use of the soft tissue ultrasonography in establishing the extent and the evolution of an injury can be of great value, and should be included in the principles of management of bite wounds, such as those proposed by Goldstein [13]. Features of fat necrosis are not well known beyond breast surgery [14, 15], but trauma of the fatty tissue can lead to severe complications, such as fat embolism [16]. We believe that the value of ultrasound in dermatology is underestimated and should be included in the assessment and management of crush injuries in the future.

REFERENCES

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