Risk factors for functional deterioration in a cohort with late effects of poliomyelitis: A ten-year follow-up study

2.1 Participants

Participants in the study were 82 patients who attended the post-polio clinic in the Physical Medicine and Rehabilitation Department at Hadassah Mount Scopus Medical Center in Jerusalem, and participated in our previous study, ten years earlier (Schwartz et al., 2014). The inclusion criterion was a diagnosis of previous paralytic poliomyelitis, with confirmation by clinical examination and EMG. Cognitive ability to participate in the study was evaluated using the short portable mental status questionnaire (SPMSQ) (Pfeiffer, 1975). The exclusion criterion was evidence of other neurological diseases that could explain the neurological impairment. A message was sent to all 197 patients who participated in the previous study, in 2009, and those who answered were scheduled for a phone interview to complete the survey. The study was approved by the Institutional Review Board of Hadassah Medical Center. All participants provided consent by agreeing to complete the questionnaires.

2.2 Survey instruments

2.3 Statistical methods

Descriptive statistics for continuous variables are presented as means and standard deviations (SD), and categorical variables as frequencies and percentages. We used a two-sided Wald test to compare responses provided in 2009 and 2020 for categorical data (there were no continuous comparisons required at this stage). We calculated average total ADL scores and scores for each element separately, for 2009 and 2020. We compared the averages using two-sided paired t-tests. We also calculated the average change in ADL between the years for different subgroups, and compared the changes using two-sided t-tests. We conducted a linear regression for the change in ADL between 2009 and 2020, adjusting for different demographic, functional, and medical parameters separately. A final regression included all parameters with a statistical significance of p < 0.3. Statistical significance was set at p < 0.05. All analyses were performed using R 3.5.0.

3.1 Demographics, comorbidities, and vascular risk factors

The demographic data of the cohort of 82 patients with LEoP, followed up for ten years, is shown in Table 1. In 2020, the mean age of the cohort was 67 years, 52.4%were men, and 79.3%were Jews. A third were still employed, similarly to the 2009 data, and the same percentage of the cohort were still physically active.

The prevalence of comorbidities (hypertension, diabetes, heart and lung disease), of vascular risk factors (smoking and BMI), and of the characteristics of poliomyelitis found in 2009 are presented in Table 2. High percentage of our participants presented vascular risk factors such as obesity, smoking, and sedentary life style, and vascular comorbidities such as hypertension, diabetes, and heart diseases. More than 60%suffered from chronic joint and/or muscular pain. Regarding the onset of poliomyelitis, 85%were infected with paralytic poliomyelitis between one to three years of age, and almost 20%presented with paralysis of both upper and lower limbs. More than 70%underwent orthopedic intervention for limb or spine correction, and more than 60%needed orthotics devices, such as ankle foot orthoses (AFO) or knee ankle foot orthoses (KAFO) in childhood. In 2009, more than 60%used AFO or KAFO orthoses, and one third used wheelchairs.

The change in ADL functions of 82 participants during ten years follow-up is presented in Fig. 1. Total ADL worsened significantly, reflecting the worsening of LEoP symptoms. Outdoor walking, indoor walking, and eating deteriorated significantly, whereas bathing and dressing did not change.

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Fig. 1

Comparison of ADL function of 82 poliomyelitis patients followed up for ten years, 2009 and 2020.

The associations between the various demographic parameters, comorbidities, and poliomyelitis characteristics, and the change in ADL functions are presented in Table 3. The only significant parameters that affected the deterioration in ADL were ethnicity and the use of a wheelchair in 2009. Reports of the use of orthotics in childhood was also related to greater deterioration in ADL, but it did not reach statistical significance. None of the other parameters correlated with deterioration in ADL.

To determine the effect of specific variables on the deterioration in ADL functions, we conducted a regression analysis. As shown in Table 4A, older age and non-Jewish ethnicity were the only demographic parameters that were associated with greater deterioration in ADL functions. All other variables showed no correlation with the deterioration (data not shown). Of the poliomyelitis-related parameters, only the use of orthotics in childhood and use of a wheelchair in 2009 were associated significantly with deterioration in ADL functions in 2020 (Table 4B). None of the other poliomyelitis characteristics correlated with the deterioration. When we add all the parameters with statistical significance above 0.3 into the model, ethnicity, the use of orthotics in childhood and the use of a wheelchair remained significantly associated with deterioration in ADL functions, whereas age was only marginally associated (Fig. 2).

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Fig. 2

Regression analysis of risk factors for deterioration in ADL.

4.1 Effect of ethnicity on poliomyelitis

Our study also showed that individuals of ethnic minority with LEoP displayed greater deterioration in functional level than did the ethnic majority population. Similar finding was observed in a study from Sweden, in which minority patients with LEoP had more severe forms of the diseases than did native Swedish patients (Werhagen & Borg, 2016). Moreover, a similar difference in level of functional dependence was found between poliomyelitis patients from countries with marked difference in socioeconomic status: Norwegians and Estonians (Rekand et al., 2003). A possible explanation of such differences between ethnic populations of people with LEoP lies in differences in cultural and socioeconomic status.

4.2 Effect of poliomyelitis history and characteristics on ADL deterioration

The study found that only the use of orthotics in childhood was associated with the functional deterioration of people with LEoP. All other parameters related to the history of poliomyelitis, including age at initial infection, extent of limb involvement, presence of scoliosis or breathing problems, and orthopedic surgery in childhood did not correlate with the progression of LEoP. Similarly to our previous study, we found no correlation between age at polio onset and the severity of polio sequelae (Schwartz et al., 2014). Other studies reported a similar absence of association (Nollet et al., 2002; Trojan & Cashman & Shapiro & Tansey & Esdaile, 1994), except for one study that found an association between post-polio syndrome and early age of polio onset (Ragonese et al., 2005). We suggest that age at the onset of paralytic poliomyelitis has a minor effect of functional deterioration in people with LEoP. By contrast, according to our results, severity of the primary neurological involvement, as reflected in need for orthotics in childhood and the use of a wheelchair in adulthood, attesting to severe neurological involvement, had a significant effect on functional deterioration. The use of orthotics in adulthood, however, was not correlated with higher deterioration in ADL functions because orthotic devices are usually prescribed to restore function and prevent falls. Thus, our findings suggest that the use of orthotics in childhood is a marker of disease severity and has a long-term effect on the functional capacity of individuals with LEoP, whereas orthotics used in adulthood may have some protective effect against functional deterioration (Genêt et al., 2010).

Scoliosis was found in 54.4%of our patients, compared to 65%in a cohort of 85 patients with LEoP in Norway (Farbu & Rekand & Gilhus, 2003). Respiratory involvement was reported in 25.9%of the participants in our study, as compared to only 7%in the Norwegian cohort. Yet, neither of these symptoms was associated with deterioration in ADL functions, suggesting that their severity was not high enough to cause functional deterioration.

4.3 Comparison with other longitudinal studies of people with LEoP

Several studies have examined the progression of the disability of people with LEoP and examined the influence of diverse factors on the rate of progression. Three earlier follow-up studies of 15 years (50 subjects), 4 years (106 subjects), and 1 week to 3 years (96 subjects) reported minor-to-modest changes in walking tests, perceived physical mobility, upper limb functioning, and muscle strength (Klein et al., 2008; Sorenson & Daube & Windebank, 2005; Willen & Thoren-Jonsson & Grimby & Stibrant Sunnerhagen, 2007). Other more recent studies found similar deterioration over 5 to ten years (Bickerstaffe & Beelen & Nollet, 2015; Flansbjer & Brogardh & Horstmann & Lexell, 2015; Stolwijk-Swüste & Tersteeg & Beelen & Lankhorst & Nollet, 2010). Stolwijk-Swüste et al. described the functional course over 5 years of 168 patients aged 45 to 85 years with LEoP and found that despite a reduction in muscle strength, disability increased little during this period (Stolwijk-Swüste & Tersteeg & Beelen & Lankhorst & Nollet, 2010). In their study, similar to our finding, increased age had a negative effect on disability, attesting to the phenomenon of accelerated aging in people with LEoP. In this study, as opposed to our finding, comorbidity affected the course of functional independence, but only the cumulative effect of comorbidities, as measured by the cumulative illness rating scale (CIRS), was associated with greater deterioration in functioning, not the specific comorbidities examined in our study. The rate of functional deterioration was examined using the progression in the Functional Independence Measure (FIM) score, which was 1.8%over 5 years and occurred in the motor items of the instrument. In our study, the rate of progression over 10 years was markedly higher, 13%, and it was manifest mainly in the daily mobility functioning of indoor and outdoor walking, not in personal care. This difference can be explained by the fact that we used a self-reporting scale for ADL evaluation, and they used the FIM index, which is based on caregiver observation. Another possible explanation is that according to a comparison between functional scores of the two cohorts, ours was more disabled, whereas the Stolwijk-Swüste’s cohort scored in the upper range of FIM, reflecting minimal disability (Stolwijk-Swüste & Tersteeg & Beelen & Lankhorst & Nollet, 2010). Another factor that contributed to the functional deterioration in the Stolwijk-Swüste’s study was the severity of leg paresis, this may be equivalent to our finding that people with LEoP who used wheelchairs, deteriorated significantly more than those who did not use wheelchairs.

4.4 Limitations of the study

Our study has several limitations. The number of patients who participated in both the original and the present study was relatively small, reflecting the attrition over the ten-year period between the two surveys and the difficulties in reaching all patients. Furthermore, poliomyelitis patients who attend our post-polio clinic present with more severe symptoms than do Israeli poliomyelitis patients in general, therefore a selection bias may reduce the external validity of the findings. Our survey was conducted by phone and used self-report scales, therefore it shares the limitation of other studies using a similar method. Yet, the ten-year within-subject design of the study enabled us to obtain important and unique information about the state of individuals with LEoP.