Sacrocaudal (sacrococcygeal) intervertebral disc protrusion in 2 cats

Abstract

One cat was presented for investigation of urinary retention and constipation and a second cat was presented with decreased appetite, reluctance to jump, reduced level of activity, and constipation. Magnetic resonance imaging revealed dorsal bulging of the hypo-intense intervertebral disc at S3-Cd1 on fast spin echo T2. Dorsal laminectomy was performed and both cats recovered with resolution of neurological signs.

King and Smith (1) reported both Hansen type 1 (extrusion) and type 2 (protrusion) intervertebral disc disease (IVDD) in as many as 1 of every 4 cats in a cadaveric study performed in a population with no related neurological signs. The relevance of this postmortem finding in live animals remains uncertain, however, as prevalence of clinically affecting IVDD in cats has been estimated to be between 0.02% and 0.24% (2–4). In cats, degenerative IVDD is considered a rare disease (4).

In the veterinary literature, the most frequently reported locations for IVDD among clinically affected cats are T13-L1, L4–L5, and L7-S1. This is likely associated with stance configuration and range of motion of the spine in the cat (5). While there are sporadic reports of sacrocaudal (sacrococcygeal) and caudal (coccygeal) IVDD in dogs (6–8), to the authors’ knowledge disc disease in the caudal (coccygeal) spine has never been reported before in cats either in postmortem studies or in clinically affected animals.

Signalment, neurological signs, magnetic resonance imaging (MRI) findings, surgical treatment, and long-term post-operative follow-up of 2 cats with a final diagnosis of sacrocaudal (sacrococcygeal) intervertebral disc protrusion is described herein for the first time.

Case descriptions

Case 1

A 10-year-old, neutered male, Bengal-cross cat was presented for neurological examination after 2 wk of urinary retention. The cat had a 6-year history of intermittent constipation as a result of a pelvic fracture managed with conservative treatment. Before referral, the cat had been hospitalized at the referring veterinary practice for 2 wk with frequent draining through an indwelling urinary catheter. Adjunctive treatment with meloxicam, dantrolene, and prazosin at unknown dosages had not resulted in clinical improvement and the referring veterinarian did not observe any voluntary urination during this time.

Physical examination revealed a thickened, alopecic, and ulcerated area at the ventral aspect of the base of the tail, thought to be a self-induced traumatic lesion caused by prolonged licking of the area. The bladder was over-distended and manual expression was not possible. On neurological examination, hypotonic anal sphincter, reduced perineal and bulbo-cavernous reflexes, and pain at palpation of the lumbosacral area of the spine were observed. Sensory and motor function of the tail were preserved, although the cat was reluctant to move the tail and slight pain was elicited on manipulation.

Case 2

A 2-year-old, neutered male, domestic shorthair cat was presented with a 1-month history of reduced appetite, reluctance to jump, reduced level of activity, pain at extension of the pelvic limbs, and transient constipation. The cat had no outdoor access and no history of trauma was reported. The cat was initially seen at the referring veterinary practice where it was prescribed a 3-week course of meloxicam at an unknown dosage with an unsatisfactory response and micro-enemas to promote defecation.

Physical examination was unremarkable. Neurological examination was unremarkable apart from reluctance to move and pain being elicited at palpation of the lumbosacral area of the spine and on tail manipulation. Sensory and motor function of the tail was preserved.

Diagnostic tests

For cat 1, a complete blood (cell) count (CBC) revealed a mild nonregenerative anemia with reduced red blood cell count [4.70 × 10¹²/L; reference interval (RI): 7.00 to 11.60 × 10¹²/L], hemoglobin 71 g/L (RI: 9.0 to 14.0 g/L), hematocrit 0.210 L/lL (RI: 0.29 to 0.46 L/L); the serum biochemistry was unremarkable. Urine analysis was conducted on a sample collected via cystocentesis and showed evidence of urinary tract infection with isolation of Enterococcus faecalis that was susceptible to Amoxicillin/Clavulanate.

In cat 2, a CBC and serum biochemistry were performed before referral and were unremarkable. Survey spinal and pelvis radiographs were taken at the referring practice. These were reviewed at admission by a Board-certified radiologist (OT) and showed faint mineral opacity superimposed over the intervertebral disc space of S3-Cd1 extending dorsally over the ventral aspect of the spinal canal.

Neuroanatomical localization for both cats was at the level of the lumbosacrocaudal (coccygeal) area. Thus, both cats had MRI of the lumbosacral spine performed (Aperto, 0.4T; Hitachi Medical System, Wellingborough, UK).

In cat 1, sagittal T2-weighted fast spin echo (FSE) and short TI inversion recovery (STIR), transverse T2-weighted FSE were included. A kyphotic angulation of the spine at S3-Cd1 was noted with ventral deviation of the tail. The intervertebral disc at S3-Cd1 was hypo-intense and severely protruded dorsally. Almost complete focal attenuation of the epidural fat was present, presuming associated spinal nerve root compression. Other findings at MRI included a markedly fluid distended bladder reaching the caudal aspect of L2, the distal portion of the descending colon distended with fecal material measuring 1.5 × L7 in diameter, and narrowing of the pelvic canal as a result of axial displacement of the right hemi-pelvis (Figure 1).

Figure 1.

T2-weighted fast spin echo sagittal (left) and transverse (right) magnetic resonance images of sacrocaudal vertebral column at S3-Cd1 (asterisk). Kyphotic angulation of the spine is noted at this level with entire degeneration of the intervertebral disc and dorsal protrusion. Focal attenuation of the epidural fat is present in trans T2. Bladder (B) is markedly distended.

In cat 2, transverse T2-weighted FSE, sagittal T2-weighted FSE and STIR sequences were included. All intervertebral discs maintained a hyperintense nucleus pulposus with the exception of S3-Cd1, which was hypointense and protruding dorsally. Mild spondylosis deformans was noted at this disc space. A slight angulation of the vertebral column in this region was noted, with reduction of the dorsoventral height of the canal, and presumed associated spinal nerve root compression. Furthermore, transitional vertebrae were noted at the lumbosacral junction with sacralization of L7 (Figure 2).

Figure 2.

T2-weighted sagittal (left) and transverse (right) magnetic resonance images of sacrocaudal and caudal vertebral column. Mild spondylosis deformans with degeneration of the nucleus pulposus is noted at S3-Cd1 (asterisk). Incomplete fusion of the second and third sacral segment with a vestigial intervertebral disc in-between is visible. In T2 trans there is reduction of dorsoventral height of the canal and associated spinal nerve root impingement. Transitional vertebra at LS with sacralization of L7.

Treatment and clinical outcome

In light of the MRI findings, disc protrusion at the sacrocaudal (sacrococcygeal) disc space was considered a possible cause for the presentation. Dorsal decompressive laminectomy with fenestration in cat 1, and dorsal decompressive laminectomy alone in cat 2 were elected as the treatments of choice.

Postoperative medications for cat 1 included diazepam (Valium; Actavis, Whiddon Valley, Barnstaple, UK), 1 mg PO, q8h; prazosin (Hypovase; Pfizer, Tagworth, UK), 0.1 mg/kg body weight (BW), PO, q12h, bethanecol (Myotonine; Glenwood, Munchen, Germany), 0.5 mg/kg BW, PO, q12h, for 2 mo, meloxicam (Metacam; Boehringer Ingelheim, Bracknell, United Kingdom), 0.05 mg/kg BW, PO for 5 d, gabapentin (Summit Veterinary Pharmaceuticals, Kidlington, Oxfordshire, United Kingdom), 5 mg/kg BW, PO, q8h to 12h for 3 d, amoxicillin/clavunate (Noroclav; Norbrook), 20 mg/kg BW, PO, q12h for 2 wk. An indwelling urinary catheter was left in place in cat 1 for 10 d and was drained regularly every 3 h. Urinary culture and sensitivity were repeated twice during hospitalization.

Postoperative medications for cat 2 included gabapentin (Summit Veterinary), 10 mg/kg BW, PO, q8h to 12h, diazepam (Valium; Pfizer), 1.5 mg q8h, and meloxicam (Metacam; Boehringer), 0.05 mg/kg BW, PO, all dispensed for 2 wk.

Cat 1 showed a slow but progressive improvement in neurological status and was discharged 2 wk after surgery when it regained the ability to urinate and defecate voluntarily. The last urine culture completed before removing the urinary catheter, did not show bacterial growth. At 1-month follow-up after discharge, neurological examination was unremarkable and the owner reported good mobility of the tail and regular and voluntary urination and defecation. At 24-month follow-up, the cat was still receiving lactulose daily (prescribed by the referring veterinary surgeon as part of long-term conservative management of chronic constipation), but no other episodes of constipation occurred after discharge.

Cat 2 showed rapid and marked improvement on neurological examination after decompressive surgery and was discharged 3 d after the operation; it was pain-free and voluntarily urinated and defecated. At 1-month follow-up, the cat showed mild paraparesis but there was no pain at palpation of the spine during neurological examination and the owner was pleased with the cat’s demeanor and quality of life. At a 20-month follow-up by telephone, the owner reported that the cat was leading an active and playful life with no abnormalities in gait.

The final follow-up information for cats 1 and 2 (24 and 20 mo after surgery, respectively) was obtained via telephone conversation with the owners and with the referring veterinarians. No clinical signs that could be related to caudal (coccygeal) disc protrusion ever recurred during the period considered in both cats.

Discussion

Caudal (coccygeal) and sacrocaudal (sacrococcygeal) IVDD have been reported sporadically in dogs (6–8), in which most of the animals were affected by disc extrusion. Clinical presentation for dogs with sacro/caudal (coccygeal) IVDD was mostly pain-related. Clinical signs in these dogs included pain associated with defecation, abnormal tail carriage, and pain elicited on manipulation of the caudal lumbosacral area and tail during neurological examination.

In the cats herein, neurological dysfunctions were also present, such as urinary incontinence, hypotonic anal sphincter, reduction in perineal and bulbo-cavernous reflexes in cat 1, and constipation with no signs of pain during defecation in cat 2. In 1 study in cats (9), conus medullaris was found to reach at least the level of the first sacral vertebra in almost 2/3 of the cats examined, or even the junction between S1–S2 according to others (10). Beyond this point the cauda equina, which includes sacral and caudal (coccygeal) nerve roots, is encountered in the vertebral canal as far as the first caudal (coccygeal) vertebra (11).

In cat 1, urinary retention is thought to be a sequela of either pudendal, third sacral nerve and/or cauda equina compression caused by the protruded disc at S3-Cd1. Lesions of the sacral cord, cauda equina, or pelvic and pudendal nerves abolish both voluntary and reflex micturition, producing what is referred to as lower motor neuron (LMN) bladder (12,13). The bladder distends with urine, so if there is no resistance in the atonic urethralis muscle, urine continually overflows and dribbles from the urethral orifice (12). The only resistance to this overflow is the tone in the internal urethral sphincter that is controlled by sympathetic nerves via the hypogastric nerve originating in the lumbar cord. Thus, although anatomically the lesion is affecting the LMN, sometimes the bladder may be difficult to express due to increased sympathetic tone secondary either to pain or suppression of normal sensory input from stretch receptors in the detrusor due to sacral nerves lesion, leaving the unbalanced sympathetic nerve as the only functioning innervation (12). Urinary infection, detected at presentation in cat 1, was likely secondary to the neurological dysfunction of the bladder, and this is a factor complicating prognosis (12).

Cat 1 was presented with a 6-year history of intermittent fecal constipation resulting from a suspected pelvic trauma, which was controlled with conservative treatment, until sudden deterioration occurred concomitantly with urinary retention 2 wk before referral. On MRI, the pelvic canal was narrowed as a result of axial displacement of the right hemipelvis and colon diameter was considered to be borderline with megacolon. At 24-month follow-up the cat was still receiving lactulose daily, but no other episodes of constipation had occurred since discharge from our hospital.

Constipation in cat 2, although resolved at the time of referral, was reported by the referring veterinary surgeon who managed it with frequent enemas in the pre-referral period. Although never reported before, exacerbation of constipation in cat 1 and constipation showed by cat 2 may be the consequence of compression or transient neurapraxia of the pelvic nerve caused by disc protrusion at S3-Cd1. Nevertheless, it cannot be excluded that constipation was caused instead by pain or inability to raise the tail as occurs in dogs with sacrocaudal (sacrococcygeal) and caudal (coccygeal) IVDD (6–8).

At 1-month follow-up, cat 2 showed mild paraparesis that was unnoticed at the time of referral, probably due to the cat’s reluctance to move. Walker et al (14) showed that the tail is used in cats for balance regulation during locomotion as well as for upward and downward jumping. Compression of caudal (coccygeal) nerves caused by disc protrusion might have affected fine adjustments during locomotion, accounting for paraparesis still noted during the follow-up examination. This theory might also explain the reluctance to jump noted by the owner before referral. Paraparesis might have improved with time as at 20-month follow-up the owner and the referring veterinarian did not report any abnormality in the cat’s gait and paraparesis was deemed to be resolved. Other causes for mild paraparesis noted at 1-month follow-up examination are possible but unknown.

The value of MRI in caudal (coccygeal) disc degeneration has been reported in dogs (6,8). In the cats herein, a decreased signal intensity of the nucleus pulposus of the affected disc, compared to the other discs, was observed in the T2-weighted sequences. Complete focal attenuation of the epidural fat in cat 1 and reduction of the dorsoventral height of the vertebral canal in cat 2 suggested spinal nerve root compression. Magnetic resonance imaging provided detailed images of the caudal spine, allowing a diagnosis with a fair level of confidence, while radiography in cat 2 showed only subtle changes difficult to relate to the clinical presentation.

In dogs, caudal (coccygeal) discs have biochemical composition and metabolic properties similar to lumbar discs, making it likely that they undergo the same degenerative processes as discs elsewhere (8,15). Studies on caudal (coccygeal) discs in cats are lacking to our knowledge, but a similar mechanism to explain caudal (coccygeal) disc degeneration in cats may be plausible.

In cat 1, on MRI, there was a kyphotic angulation of the spine at S3-Cd1 with ventral deviation of the tail. Although subluxation was not obvious during the surgical exploration, a chronic instability at the intervertebral space cannot be ruled out as a possible cause for disc degeneration and protrusion.

The reason why caudal (coccygeal) IVDD has never been reported in cats before is unknown. Some subtle signs, such as a reluctance to jump or a reduced level of activity may be overlooked as early indicators of IVDD, as proposed by Harris and Dhupa (16) for lumbosacral disc degeneration. As well, limited access to or reluctance to seek referral for advanced diagnostic imaging may account for lack of any previous report of feline caudal (coccygeal) IVDD in the veterinary literature.

In conclusion, sacrocaudal (sacrococcygeal) intervertebral disc protrusion should be considered among other differential diagnoses in cats that are presented with urinary retention and constipation, reluctance to move and jump, and pain on manipulation of the sacrocaudal (sacrococcygeal) area. Advanced diagnostic imaging of the caudal spine, such as MRI, should be considered in these patients. Dorsal decompressive laminectomy in the sacrocaudal (sacrococcygeal) spine was very successful in the long-term period for both cats, but larger numbers of cases are required to make any recommendations. Adequate communication with owners regarding prognosis is important, especially if complicating factors, such as urinary infection, are present.