Abstract
In this report two cases of localised tetanus in two young (<1 year) intact male and outdoor DSH cats, which had been missing, are described. Clinical examination revealed severe muscular spasms on the right (case 1) or both thoracic limbs (case 2). In the latter cat, wrinkling of the forehead and mild trismus were also seen. The routine diagnostic workup (CBC, survey radiographs of the spine, CSF analysis) did not reveal any abnormalities in both cats. EMG testing on the affected muscles in the second animal showed persistent spontaneous motor unit potentials, strongly indicating tetanus. The treatment, that was symptomatic (diazepam, metronidazole) and supportive (physical therapy, assist feeding and intravenous fluid therapy) resulted in the progressive improvement of limb rigidity and the restoration of motor dysfunction in a period of 5- (case 1) and 2- (case 2) month duration.
In the cat, tetanus, which is either generalised or localised, is characterised by severe muscular spasms that may result in motor deficits, signs from the cranial nerves (e.g. protrusion of the membrana nictitans, risus sardonicus, trismus), autonomic dysfunction and eventually death due to respiratory failure (Braund 1994, Davenport 1994). The susceptibility of the cat to tetanus toxin is 2000 to 7500 times lower than in the horse and half of that in the dog, mainly because tetanospasmin cannot penetrate into the nervous tissue to bind to its specific receptors (Baker et al 1986, Greene 1998). This innate resistance may explain why the localised form, which is often associated with the presence of contaminated wounds on the limbs or reproductive tract disease in the queen (Jain et al 1982, Malik et al 1989, Greene 1998), is not uncommon in this species. The initially seen increased stiffness of the muscles close to the wound or over the entire limb (Coleman 1998, Greene 1998) may spread to the contralateral limb, or evolve into the generalised form of the disease (Jain et al 1982, Malik et al 1989).
The paucity of feline tetanus cases in the literature was the impetus to report the following two cases of its localised form that involved the front limbs and gradually resolved, although partially, within a few months.
Case 1
A 9-month old, intact male, non-vaccinated and outdoor DSH cat was admitted to the Clinic of Companion Animal Medicine, School of Veterinary Medicine, A.U.T. because of a non-ambulatory lameness at the right forelimb, of 3-day duration. The cat had been missing for the last 10 days only to return to the owner's house limping.
At clinical examination a generalised and severe hyperesthesia was noticed plus that the animal could not use the right forelimb, which was held extended caudally and resisted to the passive flexion. A healing wound was also discovered on the right side of the neck. Apart from the aforementioned abnormalities, no other findings were present upon neurological examination.
Complete blood count (CBC), survey radiographs of the entire spinal column and the affected limb and CSF analysis did not reveal any abnormalities. General anaesthesia, induced with pentobarbital, resulted in partial resolution of muscular spasms.
Case 2: Localised tetanus affecting both front limbs (spastic diplegia) which are held extended caudally.
In the advent of localised tetanus as the most tentative diagnosis, the cat was put on diazepam (Stedon; Adelco) (2 mg, BID, per os) and metronizadole (Flagyl; Rhone Poulenc Rorer) (250 mg, SID, per os) soon after its hospitalisation. Symptomatic treatment of the wound was deemed unnecessary since its healing was advanced. Physical therapy on the affected limb, applied three times per day, aimed at the prevention of muscular atrophy and joint dysfunction. After 1 week in the hospital, the degree of muscular rigidity decreased markedly, thus permitting the cat to bear weight on the right forelimb, though intermittently. The cat was subsequently sent home without further medical treatment where it continued to improve during the following 5 months, with a mild residual lameness reported at that time.
Case 2
An 8-month old, intact male and outdoor DSH cat that had been missing for 2 weeks was admitted due to the inability to use its front limbs. Clinical examination revealed depression, mild dehydration, severe spasms of all muscle on both forelimbs, which were held extended backward, and reluctance to move (Fig 1). No skin lesions indicating the portal of entry could be found on the body. Despite the motor deficits associated with the spastic diplegia of muscular origin, the cat could occasionally stand upright on its hindlimbs. The animal also presented skin wrinkling on the forehead and mild trismus, which, at any rate, did not prevent food prehension and mastication. Examination of cranial nerves, proprioception and tendon reflexes of the posterior limbs was normal. No abnormalities were detected on CBC, CSF analysis and survey radiographs of the cervicothoracic spine. Electromyographic (EMG) evaluation of the affected muscles in the anesthetised animal showed electrical motor unit discharges that persisted after the insertion of the needle and despite the partial relaxation of the muscles (Fig 2).
During the two-week hospitalisation period, this animal was also put on diazepam (2 mg, BID, per os) and metronizadole (250 mg, SID, per os). Supportive measures, including physical therapy on the affected limbs, rehydration with isotonic solutions and assist feeding, were also adopted. The cat improved markedly after the beginning of the treatment, with the signs indicating cranial nerve dysfunction first being abolished. The severe motor dysfunction showed a progressive improvement that finally ended up to an ambulatory state. After a 2-month follow-up period, only a mild stiffness was noticed on both forelimbs.
Case 2: (A) EMG tracing from the biceps brachii muscle of a normal cat. (B) Persistent EMG activity in the biceps brachii muscle of case 2 cat.
Discussion
Focal spinal cord disease and radiculoneuritis, which share common clinical characteristics with localised tetanus (Malik et al 1989) were easily ruled out in both cats because of the severity of muscular rigidity and the lack of relevant laboratory evidence. Diagnostic aids in generalised tetanus include the isolation of C. tetani from an infected focus and the determination of antitetanus antibody titres. Nevertheless, the diagnosis of its localised form remains always speculative, since both bacteriology and serology offer little to nothing in the majority of cases (Weinstein 1975, Baker et al 1986, Malik 1989, Lee & Jones 1996, Greene 1999).
Localised tetanus is more difficult to diagnose than the more typical generalised form (Jain et al 1982, Baker et al 1986, Lee & Jones 1996). Since the entry site can be easily missed and muscle spasms cannot be always elicited, diagnosis is often elusive (Malik et al 1989, Greene 1998). However, in the localised form of feline tetanus, which is usually a non-progressive clinical entity, the muscular rigidity of an entire limb in an otherwise healthy animal, the history of a deep wound inflicted within a month before the appearance of the signs and its close proximity to the affected part of the body are valuable diagnostic clues (Baker et al 1986, Malik et al 1989, Lee & Jones 1996).
It is true that the initial course of the disease remains unknown in both cats, obviously because of their outdoor lifestyle; however, it is assumed to have been of 1- to 2-week duration, which is the rule in most of the reported cases (Braund 1994, Greene 1998). The high resistance of cats to tetanus toxin, which inevitably prolongs the incubation period and the obscurity of the entry site, witnessed in the second cat, impose further difficulties in the diagnosis (Baker et al 1986, Greene 1998). This innate resistance may explain why such a deep and indolent wound is usually required for the development of the disease (Godwin 1985).
Typical tetanus symptoms in the cat include the initial rigidity of a single muscle or muscle group close to the wound, the subsequent involvement of an entire limb and, less often, the generalisation of muscular spasms (Jain et al 1982, Baker et al 1986, Malik et al 1989). When thoracic limbs are affected, continuous triceps contraction keeps the elbow in extension with the carpal join held flexed or stretched (Malik et al 1989, Braund 1994, Greene 1998), as it was the case in our first cat. In the second animal, where the disease was more severe, the spastic diplegia was accompanied by facial (forehead wrinkling) and trigeminal (trismus) nerve signalment, which, nevertheless, was mild and nonprogressive. Interestingly, trismus, a common sign in humans, is rarely noticed in animals (Jain et al 1982, Woo et al 1988).
A reliable diagnostic method is the EMG on the affected muscles (Steinegger et al 1996), where the prolongation of needle insertion activity with subsequent persistence of motor unit discharges noticed in the second cat, are considered typical in tetanus (Jain et al 1982, Braund 1994, Greene 1998). These abnormalities, first reported in humans, are the result of spontaneous firing of hyperactive and disinhibited motor neurons under the effect of the toxin (Jain et al 1982, Woo et al 1988, Malik et al 1989, Saito et al 1998); therefore they may help to differentiate human tetanus from extrapyramidal rigidity and stiff man syndrome (Jain et al 1982, Woo et al 1988).
In generalised tetanus, treatment goals may include the neutralisation of circulating toxin, wound debridement, control of the infection and the amelioration of clinical signs (Ahmadsyah & Salim 1985, Coleman 1998). Interestingly, all these steps are not required in cats with localised tetanus, especially when it is not progressive (Malik et al 1989, Lee & Jones 1996). In the cats of this report, antitoxin of human or equine origin was not given because of the relative chronicity and localisation of signs. Since the wound of case 1 had already been on the process of healing, there was no need for debridement.
Penicillin G, metronidazole, clindamycin and tetracyclines are considered effective against the vegetative form of C. tetani (Ahmadsyah & Salim 1985, Baker et al 1986, Coleman 1998, Greene 1998). Metronidazole was chosen because of its better and deeper tissue penetration. In human patients, its efficacy is higher than that of penicillin G, in terms of mortality and response to treatment (Ahmadsyah & Salim 1985, Greene 1998). Diazepam, a potent skeletal muscle relaxant, was given in an attempt to control the severe and prolonged muscle spasms (Fleming & Hill 1984, Malik et al 1989, Greene 1998). Although it was administered at lower than the suggested dosage (Malik et al 1989, Lee & Jones 1996), a satisfactory reduction of limb rigidity was noticed in both cases. In contrast, physical therapy probably added little to the successful outcome of the cats.
The localised form of tetanus in the cat usually has a favourable prognosis, even in the chronic and seemingly desperate cases. Metronidazole and diazepam, plus good nursing care may warrant an uneventful recovery despite the mild disability some animals may experience on a long-term course.