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Notes on neuropathy, self mutilation in canines
Neuropathic Disorders. Traumatic Neuropathy. The regenerative ability of a nerve is directly proportional to the degree of continuity of connective tissue structures within the nerve. In neuropraxic and axonotmesic lesions where the endoneurial connective tissue and Schwann cells remain intact, the potential for axonal regeneration is good. In neurotmesis, axonal regeneration is usually frustrated by lack of connective tissue scaffold or growth tubes. Also, scar tissue tends to interfere with sprouting axons, resulting in neuroma formation. Once an axon has grown past the point of injury and penetrates a Schwann tube in the distal nerve stump, remyelination occurs. Axonal regeneration occurs at a rate of 1 to 4 mm per day. Clinical signs of spinal nerve dysfunction are outlined in Table 2.
....Self-mutilation that results from abnormal sensation in an affected area produced by regeneration of sensory nerves can be a major complication and a poor prognostic sign. In one study involving 34 dogs and cats with nerve injury associated with fracture-dislocation of the pelvis, 81% had good/excellent limb function 16 weeks after the injury, and the outcome was the same for animals with or without surgery [424]. The authors of this report suggested that surgery be performed on animals with signs of severe pain or moderate to severe nerve injury so as to relieve the nerve entrapment, avoid further nerve damage, and assess prognosis (e.g., the affected nerve may be severely attenuated, frayed, stretched, lacerated or transected). Loss of limb function or self-mutilation occurred in 15% of animals in this study. A poor prognosis is given if limb function has not improved in 3 to 4 months in animals with lumbosacral trunk/high sciatic nerve injury [424]. Physical therapy, such as a whirlpool bath, may help to overcome circulation problems and delay muscle atrophy (see rehabilitation).
Braund's Clinical Neurology in Small Animals: Localization, Diagnosis and Treatment, Vite C.H. (Ed.). International Veterinary Information Service, Ithaca NY, 2003; A3222.0203(www.ivis.org), 2003; http://www.ivis.org/advances/Vite/braund20b/chapter_frm.asp?LA=1#Idiopathic_self-mutilation Last accessed 10/6/07
Neurontin drug insert sheet: http://media.pfizer.com/files/products/uspi_neurontin.pdf
Nerve damage is frustrating (I have personal experience: three years ago I managed to amputate three fingers on my right hand in an industrial fan; fortunately the fingers were re-attached, but nerve damage is still present. I am still able to perform surgical procedures, etc., however, a sensory deficit is still present, but improving.
If the nerve sheath and nerve were lacerated or torn, then it is imperative for the sheath to be repaired. The nerve sheath acts as a conduit and insulator for the nerve to travel within. If the sheath and nerve are not continous any longer, then the nerve simply floats and the ends can not find each other to reattach. If the free ends of the nerve sheath are brought together (via microsurgery), then the nerve has a chance to knit.
Now for the frustrating part: nerve cells have very long roots/tendrils, and it takes a very long time for the nerve root to grow back, approx. 1mm per day. These nerve roots/tendrils are rather long—even up to 2-3 feet (obviously not in your small dog, but you get the idea).
The area that was cut/lacerated/damaged that is farthest away from the main body of the nerve cell (which is closer to the spinal cord) will die. Only time will allow the regrowth of the nerve root/tendril to the area of innervation (the target muscle area/etc. where the nerve leaves its effect), and it is essential for this nerve to have a pathway of regrowth; the previously mentioned nerve sheath. Unfortunately, there are some cases where the nerve has been irreparibly damaged; in these cases nerve transplant has been attempted.
I don't have high hopes for holistic treatments because they can not mend a sheath. It is entirely possible that the nerve sheath is still intact in your dog, then it simply time before the nerve heals. If you use holistic/alternative treatments, and the nerve knits, then one may have the impression that these alternative treatments did the healing, when instead it would have occured anyway.
If you feel better using alternatives, then go ahead, but make certain nothing toxic to nerve tissue is used. Sometimes doing nothing is the better path, and letting the body heal itself.
As to the self-mutilation, there will be strange sensations from the limb, even phantom pain (where the mind feels pain from an area that really doesn't have nerve supply. The new signal issues from the damaged site (this can be a long distance from its original normal end point) and is interpreted by the brain as coming from the original undamaged site, much as an amputee who insists that he can still feel a missing limb. The nerve registers still on the brain, but the original area is non-existent.
Occasionally drugs such as narcotics are used to address this, sometimes local nerve blocks, sometimes mild electrical current to confuse the brain by sending another nerve signal, sometimes selective serotonin reuptake inhibitors (Prozac, etc.). In people, bio-feedback, etc. seems helpful.
You may need to keep the collar on your little guy for 3-6 months during the healing phase.
Take-home message: need to assess if the nerve sheath is intact (sounds like it is), and need to control self-mutilation, need to be patient and constantly reasses the little fellow. Physical therapy will be an important component of care, so that muscle atrophy does not occur, and to maintain some sense of well-being. Hope this helps.
Brachial plexus avulsion occurs in dogs, cats, and birds due to traumatic injury to the C6 to T2 nerve roots that innervate the thoracic limb. With severe extension or abduction of the limb, the nerve roots stretch or tear from their attachment to the spinal cord. Clinical signs vary with the extent of root involvement. Complete avulsion results in flaccid paralysis of the limb, anesthesia distal to the elbow, ipsilateral Horner's syndrome, and ipsilateral loss of the cutaneous trunci (panniculus) reflex. The injured animal bears little or no weight on the limb and drags the dorsal surface of the paw on the ground. Sensation to the ventral surface of the paw is spared if only the cranial nerve roots are affected. Avulsion of the caudal nerve roots causes loss of sensation on the caudal surface of the limb with variable loss on the cranial surface. There is no treatment, and the prognosis for complete avulsion is poor. Amputation of the limb may be necessary because of damage from dragging or self-mutilation. Recovery is possible in mild cases in which the roots are contused rather than avulsed
The immediate effect of injury of a peripheral nerve is a variable degree of dysfunction, depending on the severity of the injury. The mildest form of injury is neuropraxia, which temporarily disrupts function with minimal morphologic alterations in the nerve. Axonotmesis is disruption of axons without disruption of the surrounding connective tissue of the nerve. The most severe form of injury is neurotmesis, which is complete severance of the nerve. With both axonotmesis and neurotmesis, there is subsequent degeneration of the axons distal to the injury site and in a portion of the nerve proximal to the injury site.
Diagnosis of peripheral nerve injuries is based on the history and clinical assessment of the motor and sensory function of the affected nerve(s). Electromyography is often helpful in identifying denervated muscles 5-10 days after injury. Nerve conduction studies may also be useful in diagnosis.
Prognosis is guarded. With neuropraxia, complete recovery usually occurs within 3 wk. For function to return after axons are disrupted (axonotmesis, neurotmesis), the nerve must regenerate from the point of injury all the way to the innervated muscle. The growth rate of regenerating axons in the distal stump is 1-3 mm/day. Recovery is unlikely if the severed axons are substantially separated or if scar tissue interferes with axonal growth. Although various anti-inflammatory drugs have been recommended for traumatic nerve injuries, there is little evidence of benefit. Surgery to appose the nerve stumps should be performed promptly in cases in which the nerve has been sharply transected. In instances of blunt trauma, surgical exploration and excision of scar tissue may help. Surgery is often successful in horses with fibrous compression of the suprascapular nerve. Longterm management consists of physical therapy to minimize muscle atrophy and decreased mobility of joints. Bandages or splints may be necessary to help protect the affected limb.
© 2006; Merck & Co., Inc.Whitehouse Station, NJ USA. All Rights Reserved. published in educational partnership with Merial Ltd. www.merckvetmanual last accessed 10/9/07