Reviewed

CERVICAL NERVE ROOT IMPINGEMENT IN A HORSE, TREATED BY EPIDURAL INJECTION OF CORTICOSTEROIDS

Daniel Marks, VMD

S U M M A R Y

Neck pain in a horse, accompanied by cutaneous hypalgesic and anesthetic areas, was treated by epidural in- jection of corticosteroids. This has resulted in remission of all clinical signs.

H I S T O R Y

In the summer of 1996, an eleven-year-old Dutch warmblood gelding used for show jumping had a history of undiagnosed front leg lameness and very bad behavior when ridden. He did not "use his neck" when jumping, and would not turn welt, especially to the left. He ran off and got "crazy," presumably in response to pain. A neck problem was suspected and the horse was taken out of work for ten months during which time he was kept in a box stall and turned out daily in a large paddock. He was put back in work only to have a recurrence of similar signs. When the author examined him, trotting and cantering seemed to cause him to hold his neck in a fairly rigid manner. He could not easily longe to the left--held his head to the outside and pulled strongly on the longe line. A left front lameness (1/ 5) seemed to coincide with initiating protraction. Flexion tests of the left carpus and lower leg joints were negative. Nerve blocks at the level of the sesamoids had no effect. Palpation of the neck did not elicit any vertebral pain. The left splenius and longissimus capitis et atlantis exhibited increased tone and mild soreness on palpation. There was

Author's address: 59 Winding Rd., Santa Fe, NM 87505, USA. Acknowledgements: I wish to thank David Orlon, DVM, Stewart McCall, DVM, and Mr. Mike AcuSa of the ARK veterinary hospital in Santa Fe, NM, and Robert N. Schwizer, DVM, Santa Fe, N M, for their input and assistance. Ms. Elizabeth Schmidt, RN, of Santa Fe, for her help, and Irving Hinds, MD, of Santa Fe for his valuable consultation.

no obvious discomfort or deficiency in range of motion in his neck when it was bent laterally, ventrally or dorsally. He was comfortable grazing. Both sides of the neck from the second cervical vertebra to 20 cm cranial to the base of his neck were hypalgesic, with left-sided dorsal anesthesia in a band 12 cm wide, whose caudal border was about 20 cm cranial to the cranial deep pectoral muscle on the leading edge of the scapula. This dermatome is described as being supplied by the fifth cervical nerve, which emerges between the fourth and fifth vertebrae. 1

Cutaneous sensation over the rest of the body and legs was not remarkable. There were no signs of cranial nerve involvement nor of any ataxia or weakness. No attempt was made to evaluate neck strength, but there was no obvious muscle atrophy. A serum test for EPM was negative. The laryngeal slap test was not remarkable. Radiographs (which were not of truly diagnostic quality) were suggestive of an enlargement of the right C4/5 facet joint with slight articu- lar radiolucent changes. The author has seen similar changes to the facet joints as an incidental finding in clinically normal horses.

A presumptive diagnosis of dorsal nerve root impinge- ment principally involving the fifth cervical nerves was made.

Chiropractic manipulation was performed every other day for five treatments which seemed to improve him. He then longed daily with side reins and the treatments were performed PRN. He improved significantly over six weeks at which time he was longeing in medium length side reins very well in both directions. There was no sign of lameness or sensory deficit. He was then ridden daily. He did very well and was doing cavelletti and starting to jump small (3') gymnastics well. He would put his head down and chew, but was reluctant to actually take a firm contact with the bit. During this time one week courses of phenylbutazone and naproxen were both tried with no visible change. He was then longed in a chambon (which caused him to carry his

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neck extended with his nose low and forward) for six minutes, which he did willingly. The next day the original signs reappeared - - stiff neck, cutaneous anesthesia and left forelimb lameness. Acupuncture treatments were added to the manipulative treatments. The signs were gone in five days. Two weeks later, the chambon was tried again and caused a more pronounced exacerbation of signs. There was bilateral cutaneous hypalgesia from C-2 caudally and bilaterally symmetrical anesthetic areas in the dermatome as described above. The left fore lameness returned as did the impression of neck stiffness and pain. This time the condition did not change over a two-week period of very light longeing and with continuing acupuncture and ma- nipulative treatments, nor with an additional two weeks of stall rest. It was decided to attempt an epidural steroid injection.

P R O C E D U R E

After examination of a skeleton and consultation on access to the dura at the junction between the atlas and axis, 2 it was decided to enter the epidural space at this level. The distance from the skin to the spinal canal was measured on radiographs and found to be 59 mm which was corrected to 54 mm to account for magnification. A five MHz diagnostic ultrasound was used to visualize the dura. The distance to the dura measured 57 mm and to the spinal cord 61 mm. The intervertebral space was marked with a skin staple. This space was 13 cm from the caudal indentation of the nuchal crest. The horse was anesthetized and the injection site prepared as for surgery. A 14-gauge 3.8 cm (1.5 inches) hypodermic needle was introduced 18 mm cranial to the middle of the interspace and angled 15 ~ caudally. It was inserted to its full length and then removed. A 16-gauge catheter 140 mm long a was placed in the channel created by the 14-gauge needle and placed in to a depth of 50 mm. A 6 cc syringe filled with saline without

Figure 1, The needle and catheter penetrates the skin, nuchal ligament, dorsal cervical muscles, dorsal longitudinal ligament between the first and second cervical vertebrae and enters the epidural space without penetrating the dura mater.

preservative was used to ascertain the back pressure to injection. Once the back pressure decreased, the needle was advanced until a slight resistance was felt. This was believed to be the dura mater. The needle was withdrawn 4 mm at which point there was still no resistance to injection of the saline. The catheter was introduced as the stylette-needle was gradually withdrawn. The catheter slipped in to the epidural space with no resistance and was inserted to its full depth. A total of eighty milliliters of saline, without any preservatives, containing 400 mg of methylprednisolone acetate, 4.5 mg of triamcinolone ac- etate and 200 mg of gentomicin sulfate was injected slowly over approximately one minute. There was no discernible back pressure to this injection.

The anesthetic recovery was uneventful.

RESULTS

By day two after the injection the cutaneous sensation was 80% improved, i.e., the anesthetic areas were only moderately hypalgesic and the hypalgesic areas seemed normal. By day three the only cutaneous deficit was a 5 cm wide zone of hypalgesia on the right side. When longed, without side reins, he volunteered to stretch his neck with his head very low at the trot. He had never trotted in this way before except with a chambon. By day four he was longed and ridden with no sign of neck pain or stiffness, by day five the cutaneous sensation appeared normal. He has been in full work for over a year, with no recurrence of neck soreness, is going very well, and showing successfully over jumps up to five feet.

DISCUSSION

Extending the neck causes a narrowing of the neural foramina. 3 Grazing for hours at a time did not seem to have any effect. The two dramatic setbacks after longeing with a chambon might be related to the change in direction of pull on the vertebra by locomotor muscles, which are not engaged when just grazing. The brachiocephalicus, serra- tus ventralis, rhomboideus, trapezius, spinalis et semispi- nalis, multifidus dorsi and the longissimus dorsi all might fit this category, ........

Of course, this represents only one case and the diffi- culty of doing this procedure and its efficacy is yet to be demonstrated. The success with this case may prompt using this procedure with similar cases. The author also suggests the possibility of its use in managing mild cases of ataxia resulting from cervical spinal impingement ("Wobblers").

Addit ional Cases Two other cases have been treated by the above

400 JOURNAL OF EQUINE VETERINARY SCIENCE

procedure. The first was an eight-year-old Thoroughbred gelding used as a show hunter with signs of general neck stiffness, limited protraction in the left front when circling to the left at a trot and with left unilateral cutaneous anesthesia related to the fifth cervical nerve. Radiographs and EPM testing were not remarkable. He was treated once and was reported to be "all better," but was then lost to follow-up.

The other case was a twelve-year-old Thoroughbred gelding who was being started as a potential jumper. When longed, without side reins, to the right he would stretch his head low down for 30-40 steps and then would raise his neck and twist his head as if to try and find a comfortable carriage or he would go with an unconstrained head and neck position. Circling to the left he could only stretch down for five to seven strides at the trot and then elevated his head higher than normal and markedly twisted his head, usually with poll left and the nose right. Even with a normal head height, he twisted his nose to the outside on a left circle. The left front had delayed and reduced protraction at the trot when circling left. He would not bend his neck to the left when coaxed with grain, but was normal to the right. Deep palpation revealed a loss of flexibility between C5 and 6. Bilateral atrophy of the supraspinatus and in- fraspinatus muscles was apparent with the left side being the most effected. There was no instability of the scapular-humeral joints. There was intermittent bilateral anesthesia and/or hypalgesia over the shoulders, biceps and the cranial superficial pectoral muscles. This was related to the sixth cervical root. Radiographs were not remarkable. He was EPM negative on both of two serum and one spinal fluid Western Blot test. There were no other neurologic signs or remarkable reactions to standard neu- rologic tests. When jumped, he got progressively uncom-

fortable as the number of jumps increased. The jumping, which started out as effortless, become labored and he twisted his neck more. NSAID administrations, chiroprac- tic manipulation, and six weekly acupuncture treatments were of no obvious benefit.

He has been injected epidurally three times; the first brought about a partial but significant improvement (esti- mated at 50%), the second treatment, six weeks later, had no discernible effect. The third, four weeks after that, pro- duced further improvement (estimated at an additional 60%).

There is no longer any cutaneous deficit; he will bring his neck around completely to the left when coaxed, and there is no discernible lameness. The shoulder muscles have returned to normal. The horse is now in easy work (jumping 3' 6") and appears much better, but still evidences some subtle signs of cervical stiffness especially after jumping.

Additional Procedures The procedure went effortlessly on the first horse; the

next cases were not as easy to get good catheter placement. Intraoperative ultrasound and radiography were both used to facilitate placing the catheter and to confirm its position.

F O O T N O T E

aAbbocathrM -T Abbo~ Laboratories, Noah Chicago, Illinois 60064 USA

R E F E R E N C E S

1. Sisson and Grossman:AnatomyofDomesticAnima/s, 4th Edition. Philadelphia: Saunders and Co., 1953.

2. Rantanan N: Personal communication 3. Denoix J-M, PaiUoux: Physical Therapy and Massage for

the Horse, Trafalgar Square, North Pomfret, VT, 1996.

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