Refining the Portrait of Late Effects of Polio

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patient with crutches in hallway

I treat fewer patients with post-polio syndrome (PPS) than I used to. I suspect this is true for most clinicians who have a decade or two of clinical experience. As practitioners see progressively fewer cases of PPS, we are less able to evaluate a given case within a broader perspective of how this patient population generally presents and the extent of the disease’s effects on things like muscle strength, gait performance, balance and fall history, and activity levels. Clinicians, particularly newer clinicians, may never see enough cases to independently develop an accurate, comprehensive portrait of what the late effects of polio look like.

Fortunately, there are centers that still manage large numbers of patients with PPS. One of these, a rehabilitation clinic based in a university hospital in southern Sweden, maintains a database of over 300 cases. Researchers from this center have published a series of studies to describe a more complete portrait of patients who have mild to moderate PPS. This cohort is defined as individuals between 50 and 80 years of age who are able to walk at least 300 meters with or without assistive devices or lower-limb orthoses, but do not require a wheelchair as their primary means of mobility. This article summarizes some of those findings and refines the portrait of post-polio effects.

LOWER-LIMB ORTHOTIC USE

Early in my career, a mentor described a conversation he overheard in a hospital when a surgeon’s rationale for performing a surgery was questioned. “Because,” the surgeon tersely responded, “when you’re a hammer, everything looks like a nail.” I’ve always retained this conversation as a reminder that we are products of our collective experiences, and that these experiences may or may not accurately represent the bigger picture. Just as an experienced cranial orthotist might inaccurately assert that conservative repositioning will never adequately address deformational plagiocephaly because such corrected cases simply don’t present in the clinic (and why would they?), it would be easy for the orthotic community to conclude that because we ultimately brace almost every case that is referred to us for treatment, most patients with PPS utilize lower-limb orthoses. However, this does not appear to be the case.

For example, in a random selection from the Swedish database of 102 cases with a response rate of 79 percent, only 21 of 81 cases used lower-limb orthoses—with AFOs outnumbering KAFOs roughly 4 to 1.1 Similar numbers were observed in a separate cohort of 122 individuals extracted from the same database.2 Interestingly, this lower-than-anticipated use of lower-limb orthoses may not be entirely due to a lack of need. In a third trial, examining the relationship between muscle strength and gait performance, the strength of the more affected knee extensors were, on average, 35 percent weaker than the less affected extensors. More strikingly, the more affected dorsiflexors were, on average, 62 percent weaker than the less affected dorsiflexors. In fact, more than half of the 90 subjects included in the study had no measurable strength in the dorsiflexors of at least one limb, yet only 21 subjects walked with an AFO.3 Given the diligence with which these subjects have been managed within the rehabilitation clinic, this discrepancy would appear to be one of choice rather than a lack of access. Many patients in this population who might reasonably benefit from lower-limb orthoses choose not to use them.

MUSCLE STRENGTH

As with many of the characteristics reported upon, the variability in observed muscle strength is considerable. Among the 90 patients with PPS who were assessed using isokinetic dynamometry, the average knee extensor strength of the more affected limb was reported at 68.4 Nm.3 However, this was observed within a sizable range of 0-185.5 Nm with a standard deviation of 45.7 Nm. Similar trends were observed in knee flexors and ankle dorsiflexors.3

Muscle weakness and muscle fatigue were the second and third most commonly reported impairments within this patient population, with self-reported impairment assessments of “quite a bit” and “extremely” by 53 percent and 51 percent of the questioned contingent, respectively.1 Yet correlations between muscle strength and a number of gait performance tests were only poor to moderate.3

These muscle strength values were correlated to a number of gait performance tests including:

  • A measure of endurance: Six-minute walk test (6MWT)
  • A measure of fast gait speed: Ten-meter walk test (10MWT), fast as possible gait (FGS)
  • A measure of comfortable gait speed: 10MWT, comfortable gait (CGS)
  • A measure of dynamic mobility: Timed Up and Go (TUG) test

As with muscle strength values, the variability in performance across these tests was considerable (Table 1). Ultimately, muscle strength appears to correlate more with measures of endurance (such as the 6MWT) and elevated walking speeds (FGS) than with comfortable gait speeds (CGS) and dynamic mobility (TUG test). However, even these greater correlations appear more limited than might be expected. The strongest correlation was observed between the strength of the more affected knee flexors and 6MWT values, but this only received an r-value of 0.65. Viewed another way, using linear regression, this means that the strength of the more affected knee flexor only explains 42 percent of the variance in 6MWT performance. This relationship increases to 47 percent when the strength of both knee extensors is considered. Adding considerations of age, gender, and body mass index (BMI) still only explain 53 percent of the variations in 6MWT performance.3

Table 1

Table 1: Observed variability in gait performance tests among patients with PPS.3

Modest, though lower, correlations were also observed between 6MWT and FGS performance and the strength of the knee flexors and extensors. Correlations between 6MWT and FGS values and dorsiflexor strength were still weaker, reported at 0.49 and -0.46, respectively. Regression analysis suggests that ankle dorsiflexor strength explained less than one-quarter of the variance observed in these two gait assessments. However, this may have been due to the use of an AFO by one-quarter of the subjects during the walking tests, which would have accommodated somewhat for strength deficits.3

By contrast, relationships between muscle strength and comfortable gait speeds were more modest. Regression analysis suggests that only 21 percent, 26 percent, and 14 percent of the variations observed with CGS could be explained by differences in knee extensor, knee flexor, and dorsiflexor strength, respectively. Even with the additional considerations of age, gender, and BMI, less than onequarter of the variations in CGS could be explained, begging the question of which other variables may be contributing.

REPORTED LIMITATIONS

Limitations are commonly reported by patients with PPS. Among a cohort of 122 subjects who were asked, “In the past two weeks how much has your post-polio limited you?” the following areas were frequently identified:2

  • Limited your ability to run?
    Quite a bit (18 percent)
    Extremely (58 percent)
    Total 76 percent
  • Limited how far you were able to walk?
    Quite a bit (36 percent)
    Extremely (16 percent)
    Total 52 percent
  • Made you concentrate on your walking?
    Quite a bit (30 percent)
    Extremely (19 percent)
    Total 49 percent
  • Increased the effort needed for you to walk?
    Quite a bit (36 percent)
    Extremely (11 percent)
    Total 47 percent
  • Affected how smoothly you walk?
    Quite a bit (33 percent)
    Extremely (13 percent)
    Total 46 percent
  • Slowed down your walking?
    Quite a bit (30 percent)
    Extremely (16 percent)
    Total 46 percent
  • Limited your ability to climb up and down stairs?
    Quite a bit (30 percent)
    Extremely (15 percent)
    Total 45 percent
  • Made it necessary for you to use support when walking outdoors, e.g. using a stick or frame, etc.?
    Quite a bit (18 percent)
    Extremely (17 percent)
    Total 35 percent
  • Limited your ability to walk?
    Quite a bit (25 percent)
    Extremely (9 percent)
    Total 34 percent
  • Limited your balance when standing or walking?
    Quite a bit (26 percent)
    Extremely (5 percent)
    Total 31 percent

These statements were taken from the Walk-12, a self-report survey instrument. When the scores were compared against the various gait performance measures described earlier, a pattern similar to that observed with muscle strength emerged. That is, the strongest correlations between self-reported walking limitations were with 6MWT performance (0.66), followed closely by FGS (0.63), and eventually CGS (0.57) and the TUG test (0.53). Restated, those patients with fewer limitations generally demonstrate better walking endurance and greater elevated walking speeds, a notable observation given that ambulatory distances were the second most commonly observed limitation within the cohort. While similar relationships exist with comfortable walking speeds and dynamic mobility, they are less pronounced.

ACTIVITY

While ambulation with PPS has its limitations as cited above, they should not be interpreted as precluding daily activity. In their study of 81 random subjects from their database, patients with PPS walked, on average, 6,212 steps per day, well above the normative values cited for adults 60 years old or greater that ranged between about 2,800 to 4,500 daily steps. As with muscle strength and gait performance tests, considerable variability was evidenced by a daily step count, ranging from 122 to over 16,000 steps.1

Subjects were also asked to catalog their daily activity levels using the 31-item Physical Activity and Disability Survey, which breaks activities into categories of exercise, leisure time, household, and work related. Physical activity was predominantly spent in household activities such as laundry, cleaning, gardening, and home maintenance (73 percent). This was followed remotely by leisure activities (16 percent). The lower prevalence of exercise (6 percent) likely finds its explanation in the reality that in the presence of muscle weakness and fatigue, any activity constitutes a form of exercise such that for most people with PPS, targeted exercise is neither sought out nor reasonable. Given that the average age of the population was 67, the low value of work-related physical activity (5 percent) is unsurprising.1

IMPAIRMENTS

The prevalence of muscle weakness and fatigue among patients with PPS was cited earlier in this article. The full list of the commonly observed, self-reported impairments in the cohort of 81 patients follows:

  • Muscle and/or joint pain during physical activity
    Quite a bit (27 percent)
    Extremely (34 percent)
    Total 61 percent
  • Muscle weakness
    Quite a bit (36 percent)
    Extremely (17 percent)
    Total 53 percent
  • Muscle fatigue
    Quite a bit (30 percent)
    Extremely (21 percent)
    Total 51 percent
  • General fatigue
    Quite a bit (33 percent)
    Extremely (14 percent)
    Total 47 percent
  • Cold intolerance
    Quite a bit (22 percent)
    Extremely (14 percent)
    Total 36 percent
  • Muscle and/or joint pain during rest
    Quite a bit (21 percent)
    Extremely (5 percent)
    Total 26 percent
patient with crutches on sidewalk

Ultimately, subjects rated their perceived level of impairment on a four-point scale across 13 items, with an average score of 26/52.1 Unsurprisingly, a negative correlation was observed between the number of daily steps recorded on a pedometer and a subject’s self-reported impairment rating (i.e., those subjects who identity greater levels of impairment do, in fact, take fewer daily steps).1

FEARS OF FALLING

As with the domains of limitations and impairments, data regarding the prevalence of fall-related concerns has also been collected. Asked to rate how concerned they are about falling across 16 daily activities, the following activities were more frequently identified:1

  • Walking on a slippery surface
    Fairly concerned (22 percent)
    Very concerned (47 percent)
    Total 69 percent
  • Walking on an uneven surface
    Fairly concerned (32 percent)
    Very concerned (28 percent)
    Total 60 percent
  • Walking up or down a slope
    Fairly concerned (30 percent)
    Very concerned (22 percent)
    Total 52 percent
  • Going up or down stairs
    Fairly concerned (20 percent)
    Very concerned (15 percent)
    Total 35 percent
  • Walking around the neighborhood
    Fairly concerned (17 percent)
    Very concerned (4 percent)
    Total 21 percent

The generally high rates of fall concerns appear to be justified as 62 percent of the questioned patients reported having experienced at least one fall in the past year, whereas only 38 percent did not.1 Of note, a negative correlation was found between fall concern values and the amount of physical activity spent in leisure pursuits. A similar correlation was not observed between fall efficacy at household-related physical activity. Unfortunately, that means that physical activity in leisurely pursuits may be compromised when fall-related confidence is compromised.

SUMMARY

When the Swedish data is viewed collectively, a composite portrait of PPS begins to emerge. It is a tremendously variable patient group frequently presenting with muscle pain, weakness, and fatigue. Despite the obvious potential benefit of lower-limb orthoses, many individuals choose not to pursue these interventions. Mysteriously, muscle weakness is only moderately correlated to gait performance measures, with greater correlations associated with walking endurance and elevated walking speeds. Impairments, limitations, and concerns about falling are frequently reported, yet this patient population generally remains fairly active compared to other populations of older adults. Of this activity, nearly three-quarters is done in and around the home.

This portrait allows practitioners to better assess how individual patients with PPS fit within the broader post-polio population and may guide clinicians to better predict and address areas of concern and limitations.

Phil Stevens, MEd, CPO, FAAOP, is in clinical practice with Hanger Clinic, Salt Lake City. He can be reached at .

References

  1. Winberg C., C. Brogårdh, U. B. Flansbjer, G. Carlsson, J. Rimmer, and J. Lexell. 2015. Physical activity and the association with self-reported impairments, walking limitations, fear of falling, and incidence of falls in persons with late effects of polio. Journal of Aging and Physical Activity 23 (3):425-32.
  2. Brogårdh C., U. B. Flansbjer, C. Espelund, and J. Lexell. 2013. Relationship between self-reported walking ability and objectively assessed gait performance in persons with late effects of polio. NeuroRehabilitation 33 (1):127-32.
  3. Flansbjer U. B., C. Brogårdh, and J. Lexell. 2013. Muscle strength is only a weak to moderate predictor of gait performance in persons with late effects of polio. NeuroRehabilitation 33 (3):457-64.

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