Peripheral Neuropathies

Fall 2002
Volume 13, Number 2

While neuromuscular disorders are a diverse group of disorders, most are progressive and will negatively impact function and quality of life. Regardless of the underlying pathophysiology, the principles of assessment of impairment and resultant potential for disability are similar. The general principles of therapeutic exercise, functional retraining, bracing, surgical correction of deformities, use of adaptive aids, and prevention of secondary complications apply to all. Because of the multiple system involvement, unpredictability and variability of progression, a model of care that includes an interdisciplinary approach that is regularly scheduled with standard measures for re-evaluation is best.

Introduction. Neuromuscular disorders are a grouping of conditions with onset from birth to adulthood, slowly to very rapidly progressive, and associated mild to severe disability. While far from an exhaustive list,

Table 1, illustrates a classification scheme and the examples of more common disorders demonstrate the heterogeneity of this grouping. Other references list more detailed classification systems.1- 3

The clinical manifestations of neuromuscular disease (NMD) can include weakness, spasticity, atrophy and fatigue of skeletal muscle, bulbar involvement affecting communication and swallowing, restrictive lung disease, cardiac dysfunction, and cognitive deficits. As the conditions progress there are secondary problems and complications that may develop including limb contractures, spinal deformities, problems with skin integrity, bowel and bladder difficulties, respiratory infections, nutritional compromise, pain, and psychosocial issues. While not curable, NMD is treatable. Despite the diversity of conditions the approach to treatment is very much the same. This comprehensive approach to management includes: 1) drug treatments to slow or delay progression, 2) assisting the individual to maximize daily functional activities and participation in home, work, and social roles, and 3) minimizing physical deformity and secondary complications. This must be done in the context of knowledgeable counseling regarding expected effects on body structure and functioning and progression of conditions. The care provider(s) should then evaluate the individual physical, family, and social environment, identify quality and end-of-life wishes to develop shared goals for a palliative and rehabilitative process. This is done with the understanding that this is an ongoing dynamic process.

The Interdisciplinary Team. This comprehensive treatment approach is a difficult task for a single care provider. In many cases, the major impediment to institution of interventions is lack of awareness of existence or availability on the part of the patient and primary care provider. In addition, it is often not clear what the appropriate timing is for available interventions. For these reasons an interdisciplinary approach is more effective. This implies coordination of services among professionals with specific expertise. An interdisciplinary team may consist of physicians (neurology, physiatry, primary care, pulmonology, and orthopedics), physical therapist, occupational therapist, speech therapists, social workers, vocational counselor, and psychologists. Ideally all of the key personnel should be available at each patient visit. However due to constraints of reimbursement, and availability of personnel, this type of comprehensive service may only be feasible at tertiary care medical centers in larger urban areas often with support of the local service organization. When these resources are not available, a reasonable alternative would be a clinic that is scheduled at routine intervals with the patient and smaller team, such as a neurologist, a physiatrist, and a clinic administrator. Each individual being assigned specific responsibilities for education, referral and communication with other care providers, and community resources. The neurologist role is key to diagnosis, initial education regarding disease, prognosis and treatments available, and monitoring of response. The physiatrist role would be to assess impairment, restrictions in activity and participation, and environmental limitations to define functional goals. The physiatrist will refer and coordinate care with a rehabilitative team that will include at varying times therapists, social worker, case managers, equipment vendors, psychologists, other physician specialists, and home care agencies. The clinic administrator has a key role in assuring follow-through with the recommendations at the time of the clinic by communicating with third party payers, getting appropriate authorizations for referral, assisting with scheduling, and obtaining documentation for the patient record.

Evaluation of the Patient with Neuromuscular Disease. While each NMD is different with regard to presentation, course and impact on life expectancy, all essentially involve multiple organ systems with resultant activity limitations and disadvantage for participation in usual family, social, and community roles. Therefore, in addition to evaluating the affect of the disease process on the organ system, the actual impact on daily functioning in multiple areas also needs to be directly measured. These functions include, but are not limited to, ambulation, activities of daily living, communication, nutritional status, community mobility, and work performance. Table 2 illustrates use of the World Health Organization new ICIDH-2 definitions of impairment; activity restriction and participation restriction (formerly impairment, disability, and handicap) based on organ systems as a scheme for evaluation of NMD.4, 5

Regularly scheduled evaluations with defined standardized measures is the best way to consistently and comprehensively address progression and facilitate timely intervention. Measures of strength, spasticity, range of motion of extremities and spine, coordination, weight; upper extremity function and gait should be completed at each follow-up. Based on knowledge of organ involvement for each condition, additional interview and modified review of systems will determine use of other measures. This then guides referrals to therapists and other medical consultants.

Organ System Involvement. Musculoskeletal. Weakness and the Role of Exercise. It is known that physically inactive people have twice the risk of coronary heart disease than the more active population. Presumed a result of weakness that is common to all NMD, most individuals have a sedentary lifestyle and for those with more slowly progressive disorders tend to be overweight. It follows that a sedentary adult with NMD will not only have weakness from the disease itself, but additional weakness of disuse further adding to limitations and restrictions. On the other side of this concern is development of overuse weakness. This is prolonged increased weakness following strengthening exercise that result in a decline in function. There currently is insufficient research for specific exercise guidelines for persons with progressive NMD. This is in part due to the relatively small numbers of individuals with each condition. Studies that have been done often group disorders together most often based on rate of progression. Based on these studies the following guidelines are suggested: 1) For persons with slowly progressive disorders, the goal is to improve strength rather than to just retard loss with the assumption that greater strength creates more reserve to perform daily tasks and lessens fatigue. 2) A submaximal-strengthening program is appropriate for persons with NMD, but there is a risk of increasing weakness with maximal strengthening programs that includes sets of high-resistance low repetition training. 3) Modest improvements in aerobic capacity without overwork weakness or excessive fatigue can be achieved with education and training in a low to moderate intensity aerobic exercise program. 4) Stretching has benefits to maintain range of motion to enhance and preserve function and should be incorporated early and included in every exercise prescription.5

For persons with rapidly progressive disorder, there are no studies regarding the effectiveness of strengthening in this population due to variability in presentation and difficulty in interpreting results in the face of progressive weakness due to the underlying disease. Submaximal strengthening programs may delay strength loss. In more advanced weakness, simply completing daily activities may result in near maximal use of strength reserves and one must consider the effects of an exercise program on the ability to participate in a full day without excessive fatigue.

Limb Contractures. In many of the progressive NMD conditions, limb contractures are common leading to greater disability, problems with mobility, activities of daily living, and often pain. Weakness combined with spasticity and inability to achieve active joint mobilization is the most common cause of contractures. In some NMDs, contractures are due to intrinsic muscle tissue alterations, such intrinsic loss of muscle fibers, necrosis of muscle fibers, and fibrosis. Collagen and fatty tissue replace functioning muscle and when combined with positioning in a shortened resting muscle length results in contracture. Individuals with conditions that have a more gradual progressive course and are associated with more fibrosis and fatty infiltration will have more problems with contractures. Those with rapidly progressive conditions and neurogenic cause of muscle weakness tend to develop less severe contractures.7

Evaluation of cause and prevention of contracture involves the understanding of functional anatomy of muscles and joints, effects of muscle imbalances, compensatory measures developed to stabilize joints and maintain upright stance, and the effect of loss of weight bearing and static positioning. Joint range of motion should be monitored regularly with objective goniometric measurement. Management involves early referral and education regarding the importance of passive range of motion, and splinting while contractures are still mild. As weakness progresses and mobility declines additional measures such as prescribed standing and walking activities, positioning lower extremities in extension, and orthoses to facilitate function are added. Once contractures become fixed, they respond poorly to stretching programs and orthopedic surgical management may help to regain lost function or minimize the degree of limitation.

Spinal Deformities. Spinal deformity develops in several progressive NMDs. Again, effective management requires an understanding of the age of onset and natural history of spinal deformities in specific conditions. Spinal deformity is more severe in conditions with childhood onset and acquired most often in association with adolescent growth spurt. Severity also increases with age and appears to be correlated with the length of time of reliance on wheelchair.8 Progression of scoliosis further negatively impacts positioning and sitting balance, causes pain, interferes with attendant care, and exacerbates underlying restrictive pulmonary disease. While spinal orthoses are used in younger patients to provide postural support and balanced sitting, they are not thought to prevent progression. Surgical management with spinal arthrodesis and internal instrumentation is often required by the second decade but undertaken with caution. A multidisciplinary evaluation and decision making process is required due to potential impact on cardiac, pulmonary, and physical functional abilities.

Pulmonary. Breathing problems are the leading cause of mortality in neuromuscular disease.9 Respiratory problems and failure in NMD is most often insidious and results from several factors including, 1) respiratory muscle weakness and fatigue causing restrictive lung disease, hypoventilation, and hypercarbia, 2) alteration of respiratory system mechanics due to stiffness in lung and chest wall, airway secretions with ineffective cough, and chest and thoracic deformities, and 3) impaired central control of respiration most often initially presenting in association with sleep.10 Careful history taking regarding exertional dyspnea, orthopnea, altered breathing patterns would indicate respiratory muscle dysfunction whereas complaints of nightmares, morning headache or daytime drowsiness would suggest sleep-disordered breathing. These signs and symptoms can be further assessed by pulmonary function testing and sleep studies. Arterial blood gas screening is more appropriate in this population rather than pulse oximetry in order to detect hypercapnia. In rapidly progressive conditions, such as ALS, early pulmonary consultation is warranted. A number of techniques, including several forms of mechanical ventilation and physical aids to assist airway hygiene are available. Identification of appropriate use should be assisted by pulmonary consultation and based on prior discussion with the patient regarding wishes for assisted ventilation. Other critical considerations include family and community support systems, third party payment, and vendor contracts.

Cardiac. NMDs vary widely in their degree of cardiac involvement. In Charcot-Marie-Tooth, which involves the lower extremities, cardiac abnormalities are rare. In ALS cardiac involvement is most often associated with autonomic dysfunction. In DMD, cardiac problems may include cardiomyopathy, pulmonary hypertension, heart failure, arrhythmia, and mitral valve prolapse. This involvement may result in significant morbidity and mortality with a 5% incidence of sudden death.11 Knowledge of potential for involvement in each individual condition is important to set up appropriate screening and early referral. Generally EKG is the first test to become abnormal and regular screening in those at risk is prudent. In conditions where cardiomyopathy is common the next step would be to proceed with echocardiography. Documented cardiomyopathy, arrhythmia and valvular disorders should be treated by referral to primary physician and/or cardiologist for considerations for antiarrhythmics, anticoagulation for prevention of embolic events, and antibiotic prophylaxis. These cardiac conditions will also have an impact on rehabilitation in the form of altered physical capacity for sustained functional activities. Recommendations for restrictions and precautions should be obtained from the cardiology consultant. Alterations in the rehabilitation management may include earlier use of assistive devices and power wheelchairs to reduce the workload.

Cognitive. Again the significance of cognitive problems in NMD varies from no involvement to severe underscoring the need to understand the impact for each condition for purposes of counseling and goal setting. Cognitive problems appear to be quite common in Duchenne muscular dystrophy and congenital myotonic dystrophy perhaps because they have been most studied. The etiology of the cognitive problems is not clear. There is also significant additional impact of chronic progressive disease on psychosocial (eg, depression, isolation) function, educational opportunities affecting both children and adults which may cause or aggravate apparent cognitive problems. Referral to neuropsychology is helpful in sorting this out.

Nutritional Considerations. There are two ends of the spectrum when evaluating nutritional status in individuals with NMD. The increasing physical inactivity due to progressive muscle weakness and associated changes in energy metabolism can result in excess body fat and obesity. In this case weight management is indicated as excess weight further burdens breathing and already weakened muscles making function more difficult. There is little evidence of how to do this. However it would be prudent to involve a nutritionist or dietician as part of the rehabilitation team if an individualÕs obesity is felt to be negatively impacting function or quality of life.

In more advanced stages or rapidly progressive NMD patients tend to lose weight due to dysphagia and the increased time and energy to eat. When nutritional intake is inadequate, there is associated acceleration in breakdown of skeletal muscle. In this case, careful monitoring of weight and nutritional laboratory parameters helps to predict when early intervention with nutritional supplements is appropriate. Based on prior knowledge of the patients wishes, enteral feeding with a gastric feeding tube should be considered and instituted timely.

Timing of Rehabilitation and Adaptive Equipment. Overall management of progressive neurologic conditions has been divided into prospective care and expectant care.12 Prospective care involves all of the measures to maintain health, physical function and quality of life. Expectant care includes anticipation of complications that might be expected during the course of the disease. Measures instituted early can help to minimize these complications. This expectant care is facilitated by regular follow-up. Even with this type of care it is often not clear when it is appropriate to institute interventions particularly in the case of durable medical equipment that may be costly and require documentation of medical necessity for insurance benefits.

Table 3 illustrates a guided treatment approach based on assessment of impairment. Amyotrophic Lateral Sclerosis (ALS) is presented as an example with the course divided in phases and stages.13 ALS is variable in its progression. The median survival is 2.5 years post diagnosis. However with presentation of primary bulbar symptoms, the 50% survival is one year. There are however those who have a more gradual progression with survival up to 15 to 20 years. In this model there may be overlap of the stages and phases depending on severity of upper versus lower extremity involvement and the severity of bulbar involvement. Once a referral is made to a therapist or consultant, it is expected that a schedule of regular re-evaluation will be instituted to identify treatment either in a comprehensive clinic setting or another model of comprehensive care.

Address comments and questions to:

Karen Theriot, MD
701 E. Hampden Avenue, Suite 320
Englewood, CO 80113