Introduction

A 13-year-old 4-kg (8.8-lb) neutered female domestic shorthair cat was presented for evaluation of acute nonambulatory tetraparesis. The cat was able to go outdoors and had seemed well 12 hours prior to presentation. At the time of presentation, the cat had to be carried into the hospital because it was unable to walk. General physical examination did not reveal any abnormalities except for low rectal temperature (36.5°C [97.7°F]). No heart murmur or pulse deficits were noted.

Neurologic examination

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Comments

Intervertebral disk disease in cats has been more frequently identified in recent years. Whereas feline infectious peritonitis and lymphoma were the most prevalent causes of spinal cord disease in cats in a 2004 study,¹ other contemporary and more recent studies^2,3,4,5 have identified several other causes of spinal cord disease in cats, many of which are more common nowadays than the still-encountered feline infectious peritonitis and lymphoma. Traumatic ischemic myelopathy, fibrocartilaginous embolism, and intervertebral disk disease (including ANNPE, disk extrusion [hernia nuclei pulposi Hansen type I], and disk protrusion [hernia nuclei pulposi Hansen type II]) in cats have all been reported.^2,3,4,5,6 Myelomalacia is defined as gross softening of the spinal cord characterized by hemorrhagic necrosis and liquefaction of spinal cord tissue⁷; affected cats have a very grave prognosis for recovery of function, and may die.^7,8,9 Focal ascending, descending, or progressive myelomalacia in dogs with acute intervertebral disk disease has been reported quite often, and several clinical and diagnostic findings have been shown to correlate to the risk of development of myelomalacia in that species.^9,10,11,12 For cats, myelomalacia as a consequence of intervertebral disk disease is uncommonly reported, although it is logical that it might indeed develop, as was evident in the case described in the present report. Myelomalacia is the result of primary and secondary injury to the structures of the spinal cord.¹³ In instances of ANNPE, the primary injury is physical, and could theoretically range from concussion or contusion to laceration depending on the velocity of the extrusion of the nucleus pulposus. Laceration of the dura and possibly the spinal cord could give rise to an intradural-intramedullary intervertebral disk extrusion.⁶ Secondary injury, which develops after the primary insult through various mechanisms, resulting in further neuronal and neuroglial damage is still a subject of research but seems to be the result of a combination of several factors including excitotoxicosis, ischemia, and ischemic-reperfusion injury.¹³ Such processes may be contained at the site of the primary injury or may spread cranially or caudally, for reasons that are not quite clear. Deterioration of the clinical status of dogs that develop myelomalacia usually ensues rapidly after onset of the first clinical signs, but a delay in onset of progressive deterioration (days after acute spinal cord injury) has been reported.^7,8,9,10

In the case described in the present report, deterioration of the cat's clinical condition was noticeably swift within approximately 10 hours after presentation. Also, cervical hyperesthesia was mild at presentation (presence of cervical hyperesthesia is not consistently reported for veterinary cases of ANNPE) but increased in severity despite administration of an analgesic drug. The subdural hemorrhage encountered during postmortem examination might explain this finding because tension or pressure on the meninges would be expected to be quite painful.

As stated previously, ANNPE in cats has been reported,⁶ and findings of more extensive postmortem and histopathologic examinations would have been ideal to confirm the nature of the gel-like substance encountered macroscopically in the cat of the present report. Such examinations could have confirmed that the gel-like substance was indeed nondegenerated nucleus pulposus material, and would have provided opportunities for investigation of possible concurrent pathological changes in the spinal cord (eg, vascular obstruction [fibrocartilaginous embolism]).

The MRI findings in dogs with ANNPE have been elaborately documented in the veterinary medical literature, and comparable findings would be expected in feline cases.^11,12 In dogs with thoracolumbar intervertebral disk extrusion, MRI findings have prognostic value related to development of myelomalacia.^10,11,12 However, the MRI findings of myelomalacia are nonspecific. In the case described in the present report, MRI would presumably have revealed extensive signal changes in and around the spinal cord, but findings certainly could not have definitively confirmed the nature of those changes. The clinically noticeable deterioration of the cat's condition (most importantly, loss of nociception) was crucial for establishing the cat's prognosis, and further diagnostic testing was declined by the owner after this information became available. Earlier diagnostic imaging was unfortunately not possible due to the out-of-hours presentation of the cat and logistic issues, but it would be unlikely to have influenced the outcome in this case. The case described in the present report has illustrated the importance of repeated clinical examination of cats with neurologic conditions and the importance of postmortem examination.