Ulnar nerve deficit after catfish sting.

To the Editor: We present the case of an ulnar nerve deficit in a 12-year-old male secondary to a catfish sting. Approximately one month before presentation, the novice angler sustained a puncture wound to the right distal forearm while attempting to release a hooked catfish. He reported no immediate neurologic deficits, but gradually developed weakness in his right fourth and fifth digits over the ensuing weeks, finally losing the ability to abduct/adduct these fingers. The pinch grip strength in the involved digits was measured as 0/10, and the intrinsic right hand muscles were atrophied. Twopoint discrimination was normal and sensation was intact. Electromyography revealed no compound motor action potential response in the right hypothenar eminence or the dorsal interosseous muscles.

The distal ulnar nerve distribution was surgically explored. The nerve was exposed and external neurolysis revealed the ulnar nerve to be transected near its entrance into Guyon canal. The affected area was grossly avascular and fibrotic. The injured segment was resected and reconstructed with a right lateral antebrachial cutaneous graft.

Microscopically, the injured nerve region was characterized by extensive fibrosis with numerous fibroblasts and few RBCs (Fig. 1). There were no obvious regenerating fibers in this region and Wallerian degeneration was obvious distally (Fig. 2). Figure 3 exemplifies the normal nerve proximal to the injury site.

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Several case reports exist in the literature (1,2) describing these injuries which occur most often in the hands and feet and range in severity from simple puncture wounds to those requiring extensive debridement and even extremity amputation. In North American fresh waters, these wounds are most often caused by the brown bullhead (Ictalurus nebulosus), Carolina madtom (Noturus furiosus) (Fig. 3), channel catfish (Ictalurus punctatus), blue catfish (Ictalurus furcatus), or the white catfish (Ictalurus catus). (3)

These aquatic animals have characteristic spines on their dorsal and pectoral fins which extend when the fish becomes agitated. The spine lateral edges are decorated with microscopic venom glands which are covered by a layer of loosely adherent epithelium. When a puncture wound occurs, this epithelium is disrupted and the toxin is released into the wound. (2) It is thought that the potentially devastating nature of catfish "stings" is due not only to the effects of the toxin itself, but also to the subcutaneous inoculation of marine bacteria (3) such as Vibrio and Aeromonas species which are most often found in victims with comorbidities. (2)

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The case presented here is unique in its neurologic sequelae. The patient reported an initial hypothenar wound but denied neurologic deficit at the time of injury. Over the ensuing weeks, a progressive loss of function in the right fourth and fifth digits occurred. Upon surgical exploration, the nerve appeared to have been transected by the offending spine, but this finding conflicts with the clinical presentation. If the spine had transected the ulnar nerve initially, one would have expected an immediate deficit. Both the fibrotic histology and the patient's gradual motor deterioration suggest a toxin-mediated injury. It is conceivable that the spine had entered the epineurium partially transecting the nerve and introducing a toxin within the sheath causing a gradual fibrosis.

In general, treatment for catfish stings should involve careful cleansing of the affected area, immersion in hot water as the toxin is thought to be heat-labile, and infiltration with a long-acting local anesthetic. Tetanus prophylaxis should be administered when indicated and plain x-rays are necessary to evaluate for presence of a foreign body. (4) If complicated by debris or abscess, surgical debridement may be required. Comorbidities or cellulites obviously necessitate broad spectrum antibiotics.

Jason R. Hess, MD

Brandon G. Rocque, BS

Susan E. Mackinnon, MD

Daniel A. Hunter, RT

Division of Plastic and Reconstructive Surgery

Department of Surgery

Washington University School of Medicine 

Saint Louis, MO

References

1. Mann JW, 3rd, Werntz JR. Catfish stings to the hand. J Hand Surg [Am] 1991;16:318-321.

2. Murphey DK, Septimus EJ, Waagner DC. Catfish-related injury and infection: report of two cases and review of the literature. Clin Infect Dis 1992;14:689-693.

3. Scoggin CH. Catfish stings. Jama 1975;231:176-177.

4. Baker DH. An unusual foreign body: catfish spine. Pediatr Radiol 1997;27:585.

5. Jordan D. A Guide to the Study of Fishes, New York, Henry Holt and Co, 1905.