Neuromuscular diseases can affect; the peripheral nerve (neuropathy), neuromuscular junction (junctionopathy) or muscle (myopathy) (Figure 1). They affect not only an animal's ability to walk, but their ability to swallow and sometimes breathe in the most severe cases. Some disorders can exist alongside existing conditions which can cause complications in patient management. There are three main neuromuscular disorders seen in dogs: polyradiculoneuritis, myasthenia gravis and polymyositis.
Polyradiculoneuritis
Polyradiculoneuritis is the most common peripheral neuropathy in dogs (Cuddon, 2002) and is described as the equivalent of Guillian-Barre Syndrome in humans (Northington et al, 1981). The exact pathogenesis of disease is still unclear however it is thought to be an immunemediated mechanism targeting the myelin and/or axons of the peripheral nerves (Añor, 2014), leading to axonal degeneration and demyelination. It has been shown that lumbosacral nerve roots are often affected more severely than thoracic or cervical ones, meaning clinical signs are usually worse in the pelvic than thoracic limbs (Cummings and Haas, 1967).
Clinical presentation
Patients usually present with a short-strided gait that progresses to flaccid tetraparesis (reduced ability to move in all four limbs) or tetraplegia (complete inability to move) over 5–10 days (Añor, 2014). Most patients show some degree of dysphonia and some present with facial paralysis, but this is variable (Dewey and Cerda-Gonzalez, 2008). Patients that have polyradiculoneuritis will retain autonomic function, i.e remain bright and alert, are able to eat and drink normally and have voluntary control of urination and defecation (Añor, 2014). Once the progressive phase has passed, the patient's neurological signs stabilise and most recover within 3–6 weeks, but full recovery is not guaranteed and some neurological deficits may remain (Cuddon, 2002) The more severe the clinical signs, the longer the recovery can take (up to 3–4 months).
Diagnosis
A diagnosis is usually made based on the patient's history and/or characteristic signs (paresis/paralysis with normal urination, defaecation and behaviour), which present over 5–10 days. Lumbar cerebrospinal fluid (CSF) analysis usually reveals increased protein with normal cell count, while nerve and muscle biopsies and/or electrodiagnostic testing of nerve and muscle function provides useful supportive evidence, particularly in atypical cases.
Treatment
Despite polyradiculoneuritis being an immune-mediated disease, the main treatment is intensive nursing care and physiotherapy due to the patient being recumbent and the risk of muscle contracture. Medical treatment with corticosteroids has been found to have little/no effect on these patients (Cuddon, 2002).
Myasthenia gravis
Myasthenia gravis is a disorder of neuromuscular transmission; meaning action potentials cannot be transferred to the muscle to initiate contraction (Figure 1). It can be congenital (acetylcholine receptors are not functional/not made by the body), but is usually an acquired autoimmune disease with autoantibodies being produced that alter the function of the acetylcholine receptor (Shelton et al, 1997).
Clinical presentation
Three forms of acquired myasthenia gravis have been described in dogs: focal, generalised and acute fulminating (Añor, 2014). In the focal form, patients present with weakness of an isolated muscle group, e.g. facial muscles. In the generalised form, patients present with appendicular weakness (Dewey, 1997) and are exercise intolerant but regain muscle strength after a period of resting. Inbetween these episodes of weakness the patient is clinically normal (Dewey et al, 1997). Patients with the acute fulminating form present with sudden onset and rapid progression of severe appendicular muscle weakness, resulting in the patient often presenting non-ambulatory (Shelton, 2002). With any form of myasthenia gravis, patients can present with signs of regurgitation due to oesophageal dilation, which can lead to aspiration pneumonia.
Diagnosis
A presumptive diagnosis can be made based on clinical history and presenting signs, however the most specific and sensitive test is an immunoprecipitation radioimmunoassay to detect the presence of serum autoantibodies (Lindstrom et al, 1988; Shelton, 1998). Other methods are less sensitive and less specific, but help with a presumptive diagnosis. Thoracic radiographs should be taken to evaluate for megaoesophagus, although not all patients will have this (Shelton, 2002). Electrodiagnostics can aid with diagnosis, but may not be specific, as other neuromuscular disorders can present the same results and an anaesthetic is required in what may be a critical patient (Oh et al, 1992). The edrophonium/tensilon response test is a strong indicator of whether the patient has myasthenia gravis or not, however a negative result does not rule out the patient having the disease. The test involves the veterinary surgeon administering edrophonium (a short-acting anticholinesterase) intravenously. A short period of improvement in muscle strength is seen post-administration in patients that respond positively, i.e. they walk normally, as the drug prolongs the time acetylcholine remains in the synaptic cleft. Once the effects have worn off, the patient will return to being weak/fatigued and not want to/be able to exercise.
Treatment
Anticholinesterase therapy has been shown to be effective at improving the ambulation of canine patients with myasthenia gravis (Shelton, 2002). These drugs reversibly inhibit anticholinesterase in the neuromuscular junction, prolonging the action of acetylcholine to enable normal muscle contraction. Drugs used include pyridostigmine bromide (Mestinon, Labiana Pharmaceuticals; 1–3 mg/kg, per os (PO), every 8–12 hours) and neostigmine bromide (Prostigmin, Valeant Pharmaceuticals;, 2 mg/kg/day, PO, every 8–12 hours) (Shelton, 2002). Dosing usually starts at the lower end, increasing until an optimal effect is achieved. Side effects include: gastrointestinal signs, e.g. vomiting and diarrhoea; excessive salivation; and lacrimation (Shelton, 2002).
Immunosuppressive drugs such as corticosteroids can be used if anticholinesterases alone show no effect, but care must be taken as they can be detrimental to patient recovery. This is because at the beginning of corticosteroid treatment, you see an increase in patient weakness, which increases their susceptibility to developing or worsening aspiration pneumonia. If this occurs or the patient has severe myasthenia gravis then hospitalisation in an intensive care unit with respiratory support may be required.
Polymyositis
Polymyositis is caused by infiltration of inflammatory cells into skeletal muscle and is usually immune mediated, but can have an infectious cause or, rarely, a neoplastic cause. Toxoplasma or Neospora are the most common infectious causes (Evans et al, 2004).
Clinical presentation
Patients with polymyositis can present with a variety of clinical signs that wax and wane, especially in the initial period of the disease. The most common presentation is exercise intolerance with a stiffened gait, almost like the patient is walking on tip-toes and their step length is extremely short (Podell, 2002). Other common presentations include: muscle weakness; muscle atrophy (Figure 2); dysphonia/dysphagia (if laryngeal muscles are affected); and regurgitation associated with megaoesophagus (if oesophageal muscles are involved) (Podell, 2002). Bilateral exopthalmus may be seen in patients where the extraocular muscles are affected (Carpenter et al, 1989).
Diagnosis
Criteria for diagnosing polymyositis are not well defined in veterinary medicine and the tests recommended aim to firstly confirm myopathic disease and then rule out systemic or infectious causes (Podell, 2002). The main criteria used are the clinical signs and at least two of: an elevation in creatinine kinase on biochemistry (10x above the normal reference range), an abnormal electromyography trace with normal nerve conduction; and/or muscle biopsies showing inflammatory infiltrates. Infection should be excluded with serologic testing or polymerase chain reaction (PCR) in biopsies. As this can be a paraneoplastic condition, thoracic and abdominal imaging is recommended to exclude concurrent tumours or megaoesophagus (which will have a large impact on nursing requirements).
Treatment
Corticosteroid immunosuppression and supportive care are the main treatments for auto-immune myositis. Antibiotic therapy can be administered 24 hours before steroid therapy if aspiration pneumonia is present. The most common corticosteroid prescribed by veterinary surgeons is prednisolone at 2 mg/kg PO twice daily during the initial phase (Melmed et al, 2004). This dose should be maintained until clinical signs are improving and creatinine kinase levels have returned to normal. After this, the dose can be slowly tapered down to the lowest every other day dose that abates clinical signs. Another immunosuppressive drug that can be used is azathioprine. This can be used alongside prednisolone for patients who cannot tolerate the side effects of corticosteroids. It is usually prescribed by the veterinary surgeon at 2 mg/kg PO once daily or once every 2 days while prednisolone is tapered down. Once this is achieved, the azathioprine can be slowly tapered down as long as the patient does not relapse (Melmed et al, 2004). The main risk for these patients is aspiration pneumonia so intensive nursing care and strict feeding programmes are necessary to reduce this risk.
Nursing care
For patients suffering from neuromuscular disease there are three main complications to consider that determine how they should be nursed: aspiration pneumonia, pressure sores and muscle contracture (Table 1). These will be discussed further. Other nursing considerations can include: urine scalding, muscle wastage, weight loss and hypostatic pneumonia.
| Polyradiculoneuritis | Myasthenia gravis | Polymyositis | |
|---|---|---|---|
| Aspiration pneumonia risk | LOW | HIGH | HIGH |
| Pressure sore risk | HIGH | LOW | MEDIUM |
| Contracture risk | HIGH (young) | MEDIUM (adult) | NONE LOW |
Aspiration pneumonia
Aspiration pneumonia occurs due to inhalation of gastrointestinal contents into the lungs. The presence of stomach acid and food particulates cause an inflammatory response due to damage to the lungs (Kogan et al, 2008b). Over time this inflammation leads to a reduction in the lungs' defence mechanisms, predisposing them to bacterial infection (Tart et al, 2010).
Prevention
It is important that patients at risk from developing aspiration pneumonia are walked frequently if able to do so, or turned regularly if recumbent to prevent an accumulation of secretions on their lungs, or run the risk of aspiration due to being in one position. For patients that have megaoesophagus, e.g. those with myasthenia, it is important to have a strict feeding plan in place that all staff members are aware of; this will involve feeding the patient balls of food from a height. The upright position means the oesophagus is in a more vertical position than usual, so the food is more likely to go into the stomach rather than the lungs (Khorzad et al, 2011)
Monitoring
When nursing any patient, but especially those with neuromuscular disease or vomiting, it is important to look out for clinical signs of aspiration pneumonia including: coughing, tachypnoea, harsh lung sounds and crackles on auscultation (Waddell and King, 2010). If any of these occur, inform the clinician in charge immediately.
Treatment
Treating patients that develop aspiration pneumonia involves early administration of antibiotics, intravenous fluids, oxygen therapy (Box 1) and respiratory physiotherapy (nebulisation/coupage).
Respiratory physiotherapy
This has not been fully established in dogs and will only be helpful for those patients that can cough. The aims are to mobilise and expel the aspirated contents using nebulisation, vibration and coupage (Rosewell, 2015) (Table 2).
| Exercise | How to perform | Pros and cons |
|---|---|---|
| Nebulisation |
|
|
| Vibration |
|
|
| Coupage |
|
|
Aspiration pneumonia is one of the biggest risks for neuromuscular patients and prevention is better than cure. It is important to identify these patients as at risk and be vigilant in monitoring to allow for early diagnosis and treatment should it develop. Patients that are ambulatory and can cough are more likely to do better than those that are recumbent and cannot. One study shows there is a 48–60% mortality rate in patients with myasthenia gravis that develop aspiration pneumonia (Kogan et al, 2008).
Pressure sores
Pressure sores are common complications in recumbent patients, especially over bony prominences. They can range from mild erythema and contusions to full thickness skin necrosis (Sims et al, 2015). Sores can develop rapidly and once formed, need to be treated aggressively to prevent infection and prevent the lesion getting bigger. Patients with myasthenia gravis are also prone to developing sores on their distal limbs and digits. This is because their feet often scuff along the ground when they are taken out as they are usually unable to walk without assistance.
Prevention
It is important that recumbent patients such as those with polyradiculoneuritis are given thick, padded bedding and turned frequently, ideally every 4 hours, to prevent an increase in localised pressure on either side. Using bandages or commercial boots, e.g. Protex Pawz boots, on patients' feet will prevent any lesions forming and therefore prevent infection. They should only be used when the patient in being walked over abrasive ground and not left on all the time.
Monitoring
It is important as nurses to closely monitor recumbent neuromuscular patients for any lesions. Checklists can be used for bony prominences and feet and any lesions noted so a close eye can be kept on these at each check.
Treatment
If lesions are noticed, these areas will need additional padding to reduce pressure on the affected area. If there is tissue necrosis, bandaging may be required, depending on the area affected. Multiple layers of absorbent material over the lesion will help prevent further injury and will need to be changed daily, or more frequently if the area is likely to get soiled. If it is not feasible to place a bandage, then applying padding around the lesion margins, e.g. a donut ring bandage, will allow a reduction in pressure on the wound, while allowing for adequate aeration.
Muscle contracture
Patients with polyradiculoneuritis are at high risk of developing muscle contractures, especially if they present young, due to long periods of recumbency and immobilisation after the initial phase of the disease. This immobilisation leads to an adaptive shortening of the muscle and an adaptive shortening and inelasticity of the soft tissues causing muscle contracture. To help with this and prevent contractures getting worse, intensive physiotherapy is needed.
Beginning the physiotherapy session by gently massaging the patients' limbs helps calm the patient and get them used to having their limbs manipulated, as the rest of the physiotherapy session will be intensive. Massage also improves circulation, both locally and throughout the body and will mobilise both dermal and subdermal tissues. To perform the massage, apply light pressure to the patients' limbs in long strokes or circular movements. This can be performed for a few minutes before continuing with the remaining physiotherapy.
Passive range of motion aims to put each joint through the normal range of motion and improve joint health. To perform this exercise, the patient is placed in lateral recumbency on a padded surface. Each joint of the limb is gently flexed and extended through its normal range of motion 10–15 times. Once this is completed the limb can be put through 10–15 bicycle movements. Once one side is done, the patient can be turned and the exercises performed on the other limb. These exercises should be performed 2–3 times a day.
Another modality that can be used with neuromuscular patients is a neuromuscular stimulation machine (NMES). The application of a stimulus to the affected muscle groups can increase tissue perfusion and may aid in minimising both the onset and severity of muscle atrophy. The stimulator should be applied to the affected muscles for 5–10 minutes, once daily.
Conclusion
Prognosis for neuromuscular patients can be extremely variable depending on the severity of disease and whether complications arise. Aspiration pneumonia is the biggest risk to neuromuscular patients, so it is important to provide vigilant monitoring and gold standard nursing care to help prevent it. If it occurs, patients that receive early treatment are more likely to do well than patients where signs are missed. Nursing these patients is a challenge, but with the correct knowledge of each of these diseases and the dedication and skill to nurse and care for these patients effectively, it is possible to provide them with the best chance at recovery.