Motor neuron pathologies
postpolio syndrome and ALS
Marilyn E. Miller
Postpolio syndrome (PPS)
Postpolio syndrome (PPS) is defined as aging with poliomyelitis. Bottomley and Lewis (2008) state: ‘Diseases of the neuromuscular system … are much more responsible for the decrements seen in aging than [are] the effects of normal aging’. Researchers estimate that 33–80% of polio survivors anywhere in the world will acquire PPS (Elrod et al., 2005; Ragonese et al., 2005). The higher the age of initial onset of polio, the lower the rate of PPS. PPS is reported to be the most prevalent progressive neuromuscular disease in North America (Elrod et al., 2005), with a significantly higher rate in women than in men (Ragonese et al., 2005). The more than one million PPS survivors in the United States of America, many of whom are in their later retirement years, find that their needs are increasing as they acquire other disabilities that accompany the natural changes of aging. To help these survivors avoid complications, rehabilitation professionals need to be sensitive to some of the special issues of PPS (Bartels & Omura, 2005).
The main clinical features of PPS are persistent new weakness, muscular fatigue, general fatigue and pain. The cause of PPS onset is unknown but contributing factors may be the aging motor neuron, muscle overuse and disuse, chronic physical stress and the impact of socioeconomic conditions (Ragonese et al., 2005; Trojan & Cashman, 2005). Pain is a persistent and common problem in persons with PPS, highlighting the need for effective and accessible pain treatments for this population (Stoelb et al., 2008). Attention to an overall healthy lifestyle and prompt identification and treatment of secondary conditions before they progress to greater impairment and/or disability are important to preserve function and maintain quality of life in PPS patients (Stuifbergen, 2005).
A systematic review of research to date indicates that conclusions cannot be drawn from the literature with regard to the functional course or prognostic factors in late-onset PPS; in fact, prognostic factors have not been identified (Stolwijk-Swuste et al., 2005). Weakness of muscle itself defines the functional consequences experienced by individuals with PPS. There is little evidence that the fatigue common in PPS is related to an increase in intrinsic fatigability of muscle fibers (Thomas & Zijdewind, 2006). Thus, this PPS fatigue must be accounted for by other sources, as yet unidentified, perhaps similar to the fatigue reported by multiple sclerosis patients and other diagnoses that involve spinal motor neuron death.
Researchers (Kalpakjian et al., 2005) have developed and validated an Index of Post-Polio Sequelae (IPPS), which offers clinicians a standardized scale to assess the severity of PPS. The IPPS measures the severity of commonly reported late effects problems. IPPS (Kalpakjian, 2004) assesses the degree of severity among 12 commonly reported problems, ranging from slight (1) to extreme (5). The 12 problems are: muscle weakness involved, muscle weakness uninvolved, muscle atrophy, joint pain, muscle pain, fatigue, sleep problems, breathing problems, swallowing problems, cold intolerance, contractures and carpal tunnel syndrome. PPS is usually slowly progressive, with no specific interventions identified. However, an interdisciplinary management program is useful in controlling PPS symptoms (Trojan & Cashman, 2005). Bartels and Omura (2005) have also recommended an interdisciplinary management program that may include (i) pharmacological interventions, limited to some anticholinergic agents, dopaminergic agents or amantadine; (ii) appropriate exercises, bracing and support; and (iii) the use of speech therapy and respiratory support when bulbar or respiratory symptoms are indicated. Persons with PPS may develop dysphagia, even though no swallowing problems were present in the initial onset of polio (Silbergleit et al., 1991). Brehm et al. (2006) recommend maintaining function in individuals with PPS, focusing on stabilizing or decreasing the energy demands of physical activities with exercise programs and/or improvements in assistive devices for walking.
Of particular interest to physical therapists are the PPS findings related to gait, a significant functional determinant of personal independence. A study by Horemans et al. (2005), which investigated the relationship between walking tests, walking activity in daily life and perceived mobility problems in a PPS population in The Netherlands, documented that PPS patients do not necessarily match their activity pattern to their perceived mobility problems. This study reported that PPS patients with the lowest test performance walked less in daily life. This same study also found no significant correlation between perceived mobility problems and walking activities. These researchers further reported that walking in daily life may be more demanding than walking under standardized conditions, an important finding to consider clinically and in future research. In their study of gait, Hebert and Liggins (2005) used a knee–ankle–foot orthosis (KAFO) to compare the locked-knee joint versus the automatic stance-control knee joint in a 61-year-old male subject with PPS. This case indicated that a stance-control KAFO appears to improve gait biomechanics and improve energy efficiency compared with a locked-knee KAFO.
The study by Brehm et al. (2006) compared the energy demands of walking in adults with PPS with those of matched healthy control subjects; this was achieved by assessing muscle strength and strength asymmetry. The findings indicated a significant difference between the groups for all walking parameters. Walking speed was 28% less while energy consumption and energy cost were higher in PPS subjects than in healthy subjects. Further, the walking parameter measures were more variable for the PPS subjects than the healthy subjects. Reduced walking efficiency was strongly associated with the degree of lower extremity muscle weakness, correlated with comfortable walking speed, and accounted for 59% of the variance. This study also reported that the energy cost of walking was associated with muscle strength asymmetry. The physical strain of performing submaximal activities in relation to the severity of the polio paresis appeared to be a determinant of the change of physical functioning over time. As noted, these researchers recommend maintaining function in individuals with PPS by stabilizing or decreasing the energy demands of physical activities. Tiffreau et al. (2010) report aquatic therapy has a positive impact on pain and muscle function. While submaximal aerobic training and low intensity muscular strengthening have shown positive effects on muscular strength and the cardiorespiratory system in persons affected by PPS, in persons reporting severe fatigue it is recommended to adapt the daily exercise routine to the individual specific case.
The almost complete eradication of polio in the industrialized nations has been an important achievement in world health policy. UNICEF formed the Global Polio Eradication Initiative in 1988 and has since made dramatic strides toward its goal (UNICEF, 2006). Rehabilitation professionals and counselors must be knowledgeable about PPS and its possible impact on employment. The physical symptoms can be severe enough to significantly alter work function, impose lifestyle changes and decrease quality of life (Elrod et al., 2005). Important barriers to work participation are encountered, particularly on the components of activity and environment, from the International Classification of Functioning, Disability and Health (ICF) model (Zeilig et al., 2012). The lessons learned now from PPS survivors may serve to improve care for future PPS survivors.
Amyotrophic lateral sclerosis (ALS)
Amyotrophic lateral sclerosis (ALS), which is also called motor neuron disease and in the US is sometimes referred to as Lou Gehrig’s disease, results in neuron death in the brain and spinal cord. Dupuis and Loeffler (2009) report it is the most frequent adult onset motor neuron disorder. The AARP and ALS Association websites report there are about 30 000 persons in the US living with ALS, with 5000 new cases identified annually. Early stages cause movement problems and fatigue, progressing to immobility, respiratory failure and death. More men than women are diagnosed, about 10% is familial, although most cases are random. Although research is ongoing, within the current status for persons with this terminal diagnosis much can be done to manage the physical and emotional symptoms to maintain or enhance quality of life. Smith (2000) reminds us that early diagnosis is not always desirable and that in ALS there is a question about the reliability of clinical diagnostic methods. Further, Smith (2000) states: ‘until it is possible to alter the treatment outcome there is little to be gained by early detection’. ALS is fatal within 2–5 years, although approximately 10% of persons with ALS may live 8 years or more. The mind remains alert and in control of sight, hearing, smell, touch and taste. Bowel and bladder functions are not usually affected. The weakness in muscle groups will not be clinically apparent until a large proportion of motor units are lost.
Dadon-Nachum et al. (2011) report: ‘This motor unit loss and associated muscle function which precedes the death of motor neurons may resemble the “die back” phenomena. Studies have indicated that in the early stages the nerve terminals and motor neuron junctions are partially degraded while the cell bodies in the spinal cord are mostly intact. If cell body degeneration is late compared with axonal degenerations, early intervention could potentially prevent loss of motor neurons.’ Recent results in mouse models showed the key pathological event was the destruction of the neuromuscular junction (NMJ) rather than neuron death. These results suggest neuromuscular junction dismantlement is likely the result of chronic energy deficiency at the level of the whole organism. Krakora et al. (2012) state: ‘The importance of NMJ has received relatively little attention in ALS, possibly because compensation mechanisms mask NMJ loss for prolonged periods. … [R]esearch should focus on the potential for preserving NMJs in order to delay or prevent disease progression.’ Related is the work of Gould and Oppenheim (2011) ‘to examine the role of neurotrophic factor (NTF) and the intracellular cell death pathway in regulating the survival of spinal and lower motor neurons in the development, after injury and in response to disease’. Human stem cell replacement/gene replacement investigated by Hefferan et al. (2012) calls for ‘a more clinically adequate treatment, strategies will likely require both spinal and supraspinal targets’. While Garbuzova-Davis et al. (2008) highlight the novel finding in ALS blood–brain barrier dysfunction: ‘[Future research may] focus on motor neuron terminals in order to delay or prevent the progressive degradation.’
Simmons (2005) calls for multidisciplinary clinics to support the patients and their caregivers for symptom management to optimize quality of life in the areas of respiration, nutrition, secretions, communication, pseudobulbar affects, therapy and exercise, spasticity and cramps, pain, depression and suicide, cognitive changes, advance directives, and care at end of life. Felgoise et al. (2010) reports psychological assessment of ALS has centered around depression, hopelessness and anxiety. Because psychological health impacts lifespan and quality of life Felgoise et al. (2010) call for broadly based mental health assessment and treatment using tools such as the Brief Symptom Inventory (BSI).
The impact on caregiver wellbeing cannot be underestimated. Boerner and Mock (2012) studied ALS patients and their caregivers for associations of two components of patient suffering – patient physical symptoms and mental distress – with caregiver wellbeing and found in regression analysis there were significant associations of patient distress with caregiver negative affect. Patient support was associated with greater caregiver positive affect, and patient symptoms and support were associated with greater likelihood of caregiver benefit-finding. Boerner and Mock (2012) call for support interventions for caregivers and ALS patients to identify and address challenges in support exchanges between caregivers and patients.
ALS rarely causes pain. ALS is not considered rare, as it is found in 7 out of 100 000 persons. Most diagnoses occur at between 40 and 70 years of age. There is not yet a cure, medicines relieve symptoms and perhaps prolong survival. Exercise is also considered to prolong function and survival. Kujala (2009) states ‘there is accumulating evidence that in patients with chronic disease exercise therapy is effective in improving the prognostic risk factor profile and in certain diseases, delaying mortality’. Dalbello-Haas et al. (2008), as a result of systematic review of randomized and quasi-randomized studies of exercise in ALS using the ALS Functional Rating Scale (AFSFRS), found a significant weighted mean improvement in the exercise group compared with the control group. However, no statistically significant differences in quality of life, fatigue or muscle strength were found. The studies reviewed were too small to determine to what extent strengthening exercises were beneficial or harmful (Dalbello-Haas et al., 2008). Several studies examined by McCrate and Kaspar (2008) were found to indicate that moderate exercise improves ALS patients’ scores on functionality tests and ameliorates disease symptoms. They give ‘possible explanations for these findings as exercise induced changes in motor neuron morphology, muscle-nerve interaction, glial activation, and altering levels of gene expression of anti-apoptotic proteins and neurotrophic factors in the active tissue’.
With regard to the outlook for treating spasticity in ALS patients, Ashworth et al. (2006) provided a systematic review of treatment of spasticity. In the single randomized study that met the inclusion criteria for review, they concluded ‘individualized, moderate intensity, endurance type exercises for the trunk and limbs may help reduce spasticity in motor neuron disease’. Repetitive transcranial magnetic stimulation (rTMS) has also been examined in the treatment of ALS. To date there is insufficient evidence from systematic reviews of randomized trials to draw conclusions about the efficacy and safety of rTMS in the treatment of ALS.
Extensive lists of websites related to ALS can be found at the Medline Plus URL: www.nih.gov/medlineplus/amyotrophiclateralsclerosis.html.
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