Surgical Management of Neurologic Disorders
Although numerous neurologic diseases have been recognized in llamas and alpacas, diseases requiring surgical procedures of the nervous system are uncommon.1 The most common diseases that involve surgical interventions include injury to the spine, infection of the middle and internal ear cavities, and internal hydrocephalus.
Neurologic deficits originating in the cervical spinal cord are most commonly caused by larval migration of the meningeal worm Parelaphostrongylus tenuis.1 However, neurologic deficits occasionally are found to be associated with either congenital vertebral malformations or cervical vertebral injuries.1–4 Interestingly, intervertebral disk protrusion and discospondylitis have been diagnosed in llamas and alpacas.5–7 Prognosis associated with the surgical management of these diseases is unknown.
Many cervical injuries go unnoticed because the extensive fiber coverage of the cervical region hides cervical deviations from view. These injuries become apparent when the animal is sheared, develops an abnormal posture, or demonstrates neurologic deficits. These may not be observed for months following the injury. Acute injuries often occur when camelids are being halter trained by an inexperienced handler or when an animal becomes entrapped in a gate, fence, or feed bin. Occasionally, these injuries are caused by peer trauma.
Acute cervical injuries usually occur as subluxation of the vertebra and most often affect C3-4, C4-5, and C5-6. Usually, the camelid is presented for examination because of abnormal head and neck posture. Neurologic deficits are often mild or inapparent but may be debilitating and cause recumbency. The most common neurologic deficits are upper motor neuron (UMN) deficits to the hindlimbs, but either UMN or lower motor neuron (LMN) deficits may be seen in the forelimbs, depending on the site of the lesion. UMN signs include an exaggerated or hypermetric gait, most pronounced in the hindlimbs, and exaggerated reflexes in the limbs. Conscious proprioception deficits (e.g., stumbling, staggering, imprecise placement of feet) also may be seen. Most camelids are ambulatory when first examined but may present with paraparesis or tetraparesis.
Chronic cervical injuries often are presented for examination because of abnormal head and neck posture or difficulty grazing. Progression of neurologic deficits may be caused by progressive enlargement of scar tissue surrounding injured tissues, bone proliferation caused by vertebral fracture or osteoarthritis of articular facets, or deviation of the spine. Progressive worsening of deviation of the neck is most common in young stock after subluxation injuries when vertebral elongation and bone growth cause distortion of the spine.
Diagnosis of cervical subluxation is apparent on physical examination. However, radiographic examination of the cervical vertebral column is required to evaluate the severity of the lesion(s) and assessment of the need for surgical intervention. In chronic cases, myelography (positive contrast radiography or computed tomography [CT]) is useful to determine the location of impingement. Myelography also is indicated when radiographic findings do not match those expected based on the physical examination. When multiple lesions are expected or physical examination findings suggest multifocal neurologic deficits, myelography helps determine the need for surgical intervention. Minimum routine information includes hematology, serum biochemistry profile, and cerebrospinal fluid (CSF) analysis. CSF analysis aids in differentiating patients suffering traumatic injury from those affected by parasitic myelitis.
Candidates for conservative management are those patients having minimal to no neurologic deficits. In these cases, the owner must accept that a permanent deviation of the cervical spine will persist. Conservative management may include confinement to a stall or small pen for a period of 8 to 12 weeks, nonsteroidal antiinflammatory drugs (NSAIDs), and placement of feed and water troughs at a higher level to allow the animal ease of access during the early stages of healing. In patients having acute cervical injuries, external support of the neck may aid in lessening the severity of deviation and may minimize the extent of scar tissue formation. The simplest form of support is a modified Rover Jones bandage made from rolled cotton applied from the base of the skull to the thoracic inlet. The neck may be further strengthened by continuing the cotton onto the thorax by placing a “figure-of-8” pattern around the thorax and between the forelimbs. When rigid support is desired, the bandage may be converted to a cast bandage by using fiberglass casting tape. The casting tape is applied as four to six layers thickness. A one quarter–inch aluminum rod may be formed to fit over the dorsal thorax and along the sides of the neck to span the area between the thoracic cast and the neck cast. Additional casting material is placed to a thickness of four layers. The neck should be placed slightly elevated to the thoracic vertebral column. The fiberglass cast is maintained for 4 to 6 weeks and removed. Patients must be closely observed during the first 24 hours after application of the external bandage or cast because some llamas and alpacas do not accept this type of external support. Patients that resist neck bandaging may become severely distressed and demonstrate respiratory distress or obstruction. Rapid intervention may be needed to adjust or remove the bandage. The patient is maintained in confinement for 4 to 6 weeks after the cast is removed. Feed and water troughs should be placed at a higher level for easy access during this period. The purpose of the neck and body cast is to allow the cervical vertebral column to “stabilize” in a suitable conformation to minimize the amount of callus and scar tissue that will form. This will minimize the risk of the development of compressive lesions of the cervical spinal cord. The ventral aspect of the cranial end of the cast must be adjusted so that the head may be easily flexed without restriction.
Surgical treatment of cervical injuries is indicated in animals with debilitating neurologic deficits or progressive neurologic signs. Occasionally, the owner may desire correction of the cervical deviation for cosmetic reasons, but the risks inherent to surgery of the cervical spine must be clearly explained so that the client can make an informed decision about this option. The specific surgical approach is mandated by the location and extent of lesions documented via radiography or CT imaging. Camelids have minimal soft tissue coverage of the cervical vertebra, and therefore, the surgical approach is relatively straightforward. Surgical options include dorsal laminectomy or hemilaminectomy, external coaptation using a ring fixator assembly, dorsal stabilization using pedicle screws and bone cement, dorsal stabilization using interspinous plate fixation, and ventral vertebral stabilization using plate fixation. Clinical success rates or outcomes are not established for these procedures in llamas and alpacas. I have used all of these methods to repair various cervical injuries. All of these methods have significant risks of intraoperative and postoperative complications. Following hemilaminectomy of a chronic, progressive C4-5 lesion, acute neurogenic edema and death occurred in a llama. Respiratory failure and death occurred in an alpaca ventral stabilization of an acute subluxation of C3-4. To date, the fewest complications have been observed when surgical restoration of anatomic alignment of the cervical vertebral column via a dorsolateral approach without laminectomy has been used. In this approach, the dorsal articular facets are resected, and the vertebral bodies realigned. Two 6.5-millimeter (mm) cancellous bone screws or end-threaded positive profile pins are placed into each vertebral body, and these are connected with the use of orthopedic cement. Antibiotic impregnation of the cement is often done to minimize risk of implant infection. Application of bone plates is less desirable because the vertebral contour is complex, the vertebra have limited holding power for bone screws, and molding of the bone plate in multiple planes (minimum 3.5-mm wide) decreases its resistance to bending and torque. A neck or neck-and-body cast is placed for 30 days following surgery.
Conservative treatment has a fair to good prognosis for prevention of progression of neurologic deficits, but anatomic alignment is not restored. In my experience, camelids with neurologic deficits have a guarded prognosis with surgical intervention. Camelids with significant neurologic deficits are unlikely to improve and may worsen after surgical intervention.