The spinal cord is essentially an electrical cable. Many diseases can result in paresis or paralysis, however, the mechanisms are really limited to two: 1) the spinal cord gets compressed, or 2) something takes up space within the parenchyma of the spine. Compression injuries in small animals occur as a result of either disc extrusion (Hansen Type I) or disc protrusion (Hansen Type II); compression secondary to vertebral or meningeal tumours; or compression from spinal trauma resulting in fracture/luxation/hyperextension injury. Intraparenchymal spinal disease results from space-occupying lesions - fluid (syringomyelia); cells (neoplastic vs. inflammatory cells); or vascular injury as occurs with fibrocartilaginous emboli (FCE/"spinal stroke") or secondary to an acute concussive non-compressive disc extrusion.
The most common causes of acute spinal injury are disc extrusion and FCE. The immediate objective in acute spinal injury is to identify and remove the cause of the paresis/paralysis as safely as possible. MRI/CT/myelography are utilized to differentiate between compressive and non-compressive aetiologies. Therapeutic objectives are to alleviate compression of the spine, stabilize the spine where necessary, and provide the best opportunity for functional recovery. FCE injuries are generally self-limiting and the goal in any acute spinal injury is to maximize the functional recovery of uninjured neural elements.
Gait is classified as firstly ambulatory versus (vs.) nonambulatory paretic (tetra-, para-, mono-, or hemiparetic). Paraplegia refers to a patient with no voluntary movement in both pelvic limbs, and these patients need to be identified as either deep pain perception positive or negative (the latter carrying a poorer prognosis for recovery). Generally patients are graded on a simple scoring system of 0 - being normal, 1 - only exhibiting spinal pain, 2 - ambulatory paraparetic, 3 - nonambulatory paraparetic, 4 - paraplegic with intact deep pain perception, and 5 - paraplegic with absent deep pain perception. Urinary continence can be variable within the 4 and 5 categories.
Opioid analgesia has proven to be the most effective analgesia for neurosurgical patients, and of this category, the pure agonists are the most potent but also have more potential side effects. Preoperative administration allows for a lower postoperative requirement. The author's preference is preoperative hydromorphone or oxymorphone 0.1 mg/kg with postoperative 0.05 mg/kg q 4 h until transdermal fentanyl (patch) becomes effective - usually 12–24 h after application. Oxymorphone at similar dosages may be utilized, and in small dogs (< 6 kg) and cats, butorphanol (agonist/antagonist) is used - premed 0.05 mg/kg, then 3 mg total either SC or transdermal q 4–6 h. Fentanyl CRI is usually used intraoperatively and for the first 24–48 h postoperatively in dorsal cervical surgery.
Nonsteroidal antiinflammatory drugs (NSAIDs) provide analgesia by inhibition of cyclooxygenase enzymes, with meloxicam (0.1–0.2 mg/kg q 24 h) being the most sparing of the NSAIDs in its inhibitory effects on COX-1. Despite this, COX-2 NSAIDs can result in gastrointestinal ulceration, particularly in postoperative spinal patients. NSAIDs are reserved for those patients intolerant of opioids, with uncompromised renal and hepatic function, and not currently receiving steroids.
Gabapentin (5–10 mg/kg q 8–12 h) has been found to block nociceptive (pain) pathways at the level of the dorsal horn, and may provide relief of nerve root pain, and is used particularly in lumbosacral and cervical nerve root impingement. Methocarbamol (50–100 mg/kg q 8 h) or cyclobenzaprine (0.5–1 mg/kg q 8–12 h) for muscle relaxation are of limited benefit as analgesics unless nerve root impingement and resultant muscle spasm is evident. Additional modalities that alleviate pain include acupuncture, ultrasound and laser therapy.
Recumbent patients are predisposed to numerous complications, from decubital ulcers, skin irritation secondary to urine and faecal contamination, to muscle and joint deterioration (atrophy and contractions). Soft bedding, preferably elevated by means of a grate to prevent urine pooling, bedding materials such as artificial fleece/absorbent pads, in addition to frequent turning/repositioning q 4 h, will remove the major sources of decubital ulcers - moisture and pressure. Bladder management is not only important to reduce skin contamination but also to prevent long term micturition complications - spinal patients commonly lose bladder control and a distended atonic bladder (myogenic bladder syndrome) can result from a chronically distended bladder. Clipping of the hair around the perineal area makes for easier cleaning and the application of barrier creams to reduce irritation and dermatitis.
Lower Motor Neuron Bladder/Atonic Bladder
Lower motor neuron (LMN) injuries involve either the spinal cord segments S1–3 or the pelvic and pudendal nerves arising from these segments. Urethral and detrusor hyporeflexia result. The most characteristic sign is a distended bladder that is easily expressed. A reduced or absent perineal reflex and/or tail tone is usually evident. Invariably, urine overflow is noticed as pressure within the bladder exceeds the resistance of a non-functional sphincter ("overflow bladder"). However, this is incomplete emptying of the bladder since the detrusor muscle cannot fully contract to maintain enough pressure to prevent the urethral sphincter from closing. An intramural reflex may later develop within the detrusor muscle, but it is a weak reflex and takes time to develop. Detrusor atony occurs when the detrusor muscle cannot contract or where there has been disruption of the tight junction between smooth muscle cells. Atonic bladder as a result of disruption of the tight junctions (myogenic bladder) is a serious consequence of a lower motor neuron injury.
Management of LMN bladder/atonic bladder syndrome requires stimulation of the bladder smooth muscle. The parasympathomimetic agent, bethanechol (Urecholine®), is used to stimulate smooth muscle contractility. The dosage varies - cats: 2.5 to 5 mg q 8 h; dogs: small to medium-sized 5 mg q 8 h, large 10–15 mg q 8 h. Increments of 5 mg may be made q 8 h until effective or toxic. Bethanechol appears to be more effective where the pelvic nerve is still intact - acute over-distension, reversible compressive neurologic lesions (disc disease), and as a component of therapy in idiopathic dyssynergia. Side effects include salivation and lacrimation in mild cases, to vomiting, diarrhoea and bronchoconstriction. The drug should not be used if gastrointestinal or urinary obstruction is present. Bethanechol may cause increased urethral resistance. Cisapride (Propulsid®) has been used in people for bladder atony, and may have a role in small animals bit is increasingly more difficult to obtain. Other drugs that may have a beneficial role include pyridostigmine, metoclopramide, and propranolol.
Upper Motor Neuron Lesions/Functional Urethral Obstruction
An upper motor neuron lesion (UMN) is associated with a lack of voluntary control of micturition, and reflex hyperexcitability of the urethral sphincter due to a lack of inhibition to the somatic efferents in the pudendal nerve. A large distended bladder results that is difficult to express. Significant resistance will occur if the lesion is located between spinal cord segments L4 and S1, since the sympathetic supply will maintain alpha-adrenergic tone via the hypogastric nerve. Five to ten days after spinal cord injury, reflex micturition (automatic bladder) is initiated by an increase in bladder intramural pressure. This reflex results in incomplete voiding, and a large residual urine volume.
Functional urethral obstruction often requires pharmacological manipulation of both the internal and external urethral sphincters, while the bladder is maintained as empty as possible using intermittent aseptic urinary catheterization. Inhibition of alpha mediated smooth muscle of the internal urethral sphincter is achieved using alpha-adrenergic antagonists. Phenoxybenzamine (Dibenzyline®) is most commonly used, however, it has become increasingly more difficult to obtain and requires compounding. A dosage of 5 to 20 mg q 8–q 12 h is used in dogs or 2.5 to 5 mg q 12–q 24 h in cats. Gastrointestinal disturbances, hypotension, and incontinence are potential side effects. An alternative alpha antagonist is prazosin (Minipress®) at 1 mg/15 kg q 8–q 12 h in dogs and 0.25 mg per cat q 12–q 24 h. Since marked hypotension can result from prazosin, patients should be monitored for lethargy, collapse, pallor, syncope or seizures. The use of alfuzosin (Uroxatral©), a more selective urinary alpha antagonist) may avoid the hypotension issues. Tamsulosin (Flomax©), an alpha1A agonist is being successfully used at 0.1–0.2 mg/10 kg/day, as it is more specific in targeting the internal urethral sphincter and avoids potential hypotension. This drug appears to be more effective, and is convenient for large breed dogs - compounding is required for small breeds (available as a 0.4 mg capsule).
Striated muscle relaxants are required for inhibition of the external urethral sphincter, and include diazepam (Valium®), dantrolene (Dantrium®), and baclofen (Lioresal®). Diazepam is the most common relaxant used in dogs (usually for bladder management post disc surgery) and is usually added when alpha antagonists alone are unsuccessful. Oral doses range from 2 to 10 mg q 6–q 8 h in dogs, and 1 to 2.5 mg q 8 h in cats. Dantrolene may be used at 1 to 5 mg/kg q 8 h and is thought to be a more specific peripheral muscle relaxant with fewer side effects of sedation, hypotension, and gastrointestinal upset. Baclofen inhibits spinal reflex activity and has not been widely used in veterinary medicine.
Frequent urinalyses are required to monitor for urinary tract infections since bladder management will often circumvent the normal defence mechanisms. Inhibition of urethral sphincters, bladder catheterization, faecal contamination of the perineum, and residual urine, will all contribute to increased infection rate. Prophylactic antibiotic usage has the potential for selecting more resistant bacterial strains and is not universally recommended.
Objectives include maintaining joint range of motion, reducing muscle and joint pain, reducing muscle atrophy, and stimulation of ambulation. Physical rehabilitation can be divided into two major categories: 1) passive exercise and 2) active exercise.
Prior to initiating passive or active exercise, massage is generally performed starting with stroking, where the patient is stroked from head to toe, in the direction of hair growth. This has a soothing and comforting effect on the patient. Thereafter, kneading is performed, where pressure is exerted between the fingers and palm on one's hand, gently squeezing the muscles and proceeding in the direction of lymphatic flow.
Warm packs can be utilized to relax stiff muscles prior to exercise. Commercially available microwavable packs work well but should not be warmer than can be comfortably maintained against the inner forearm of the therapist. In addition, the pack should be wrapped in a thin towel before being placed against the patient's skin.
Passive range of motion (PROM) is performed in patients who lack voluntary movement to maintain joint flexibility - it does not improve muscle strength since active movement is required to maintain muscle mass. Flexion and extension of individual joints should be carried out with the patient in lateral recumbency and each joint gently extended and flexed through 15–20 cycles, 3–4 times daily.
Patients with voluntary movement will gain improved muscle strength and coordination by assisted walking and standing. Short sling-assisted walks 3–5 minutes 3–4 times daily without fatiguing the patient is desirable. Booties will allow for greater traction of the paws on smooth surfaces. Underwater treadmill therapy has become a major modality in rehabilitation therapy - the buoyancy of water provides a lifting effect, allowing the patient greater freedom of movement with less weight having to be carried. In the absence of an underwater treadmill, an ordinary treadmill can be utilised to good effect. Either physical barricades or two assistants are required to prevent the patient from going off either side of the apparatus. Swimming can result in fairly forceful muscle contractions and is not advised in the first 4–6 weeks post neurosurgery to allow adequate healing of the muscles adjacent to the laminectomy site.
Other modalities often used in the rehabilitation of spinal patients include acupressure, cold laser therapy, electrical stimulation (neuromuscular electrical stimulation), and acupuncture. These are useful adjuncts to a rehabilitation program but should not replace a passive or active exercise programme.
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