New neuromuscular symptoms in patients with old poliomyelitis: a three-year follow-up study

Outcomes of Colorado children with acute flaccid myelitis at 1 year

OBJECTIVE

We describe long-term functional, neurodiagnostic, and psychosocial outcomes of a cohort of 12 children from Colorado diagnosed with acute flaccid myelitis (AFM) in 2014.

METHODS

Children were assessed every 3 months for 1 year or until clinical resolution. Assessments included neurologic examination, MRI, EMG/nerve conduction studies (NCS), functional measures (Assisting Hand Assessment, Hammersmith Functional Motor Scale), and Patient-Reported Outcomes Measurement Information System questionnaires.

RESULTS

Eight of 12 children completed the study. Six of 8 had persistent motor deficits at 1 year; 2 demonstrated full recovery. Four were not enrolled, 2 of whom reported full recovery. The 6 affected were weakest in proximal muscles, showing minimal to no improvement and significant atrophy at 1 year. All patients improved in distal muscle groups. Cranial nerve dysfunction resolved in 2 of 5 and improved in all. Four of 5 showed progressive functional improvement at 6 and 12 months. Two of 8 reported pain at 1 year. Three of 8 reported depressive symptoms. Repeat MRI was performed in 7 of 8 children a median of 7 months after onset and showed significant improvement or normalization in all but one child. Repeat EMG/NCS was performed on 4 children a median of 8 months after onset and showed ongoing denervation and chronic reinnervation in 3 children with persistent deficits.

CONCLUSIONS

At 1 year, children with AFM demonstrated functional gains but weakness persisted. EMG changes correlated with persistent deficits better than imaging. Despite improvements, AFM had substantial long-term functional effects on affected children.

Post-polio syndrome: clinical manifestations and cerebrospinal fluid markers

Post-polio syndrome (PPS) refers to a constellation of new neurological, musculoskeletal and general symptoms occurring in survivors of poliomyelitis decades after acute paralytic and nonparalytic disease. The common manifestations of PPS include generalized, central and peripheral fatigue, muscle weakness and musculoskeletal pain. The pathogenesis of PPS remains obscure. Three prevailing hypotheses have been advanced: stress-induced degeneration of surviving neurons, persistent poliovirus replication or virus reactivation and immune-mediated damage. The diagnosis of PPS is based on medical history and clinical examination, since no specific diagnostic tests are available. In the light of recent studies demonstrating a partial beneficial effect of intravenous immunoglobulin, this article will focus on cerebrospinal fluid biomarkers reflecting disease activity and pathogenic processes in PPS.

A pilot study of falls, fear of falling, activity levels and fall prevention actions in older people with polio

BACKGROUND AND AIMS

Polio survivors are ageing, and reporting new complications including falls. The aims of this study were: 1) to determine the frequency of falls, circumstances surrounding them, and the consequences of falls in older people who have polio; and 2) to investigate the range of fall prevention interventions undertaken to reduce the individual's risk of falling.

METHODS

A survey was conducted of members of the Eastern Polio Support Group of Victoria. Twenty-eight respondents (70%; 7 male, 21 female) had a mean age of 66 years and an average duration of 57 years since the onset of polio. The survey addressed demographic data, mobility, frequency and description of falls over the last 12 months, their consequences, and community services utilized. The Modified Falls Efficacy Scale (MFES) and Human Activity Profile (HAP) were also completed. Comparative data on the MFES and HAP were obtained from age- and gender-matched healthy community-dwelling older people.

RESULTS

Fourteen respondents (50%) reported one or more falls over the past 12 months, half reporting multiple falls. Two-thirds of falls occurred while walking. Of those who fell, 67% did not require medical attention. The highest percentage of injuries were bruises or grazes (44%), with one fracture reported. Sixty-one percent reported being fearful of falling, with an average MFES of 7.4 (+/-2.0), compared with the average of 9.7 (+/-0.5) for the age- and gender-matched controls (p<0.05). Only 5 of the respondents reported changing their level of activity as the result of a fall. A significant difference was identified on the Adjusted Activity Score (AAS) of the HAP between polio non-fallers (mean 56.3+/-19.1), polio fallers (mean 40.1+/-15.6) and age- and gender-matched controls (mean 73.5+/-10.3) (F2,46=25.5, p=0.000). The median number of fall prevention activities undertaken in the previous 12 months was one, 11 of the 28 respondents undertaking two or more. The most common interventions implemented were vision checks (42%) and review of medications by a doctor (25%).

CONCLUSIONS

A high rate of falling, fear of falling and low activity levels exist in older people with polio. There is a need for further research and clinical programs to reduce falls and injuries in this group.

Persistent poliovirus infection of human fetal brain cells

It has been suggested that poliovirus (PV), the causative agent of poliomyelitis, could persist in surviving patients. We have previously shown that PV can persistently infect some human cell lines in vitro, particularly neuroblastoma cell lines. We report here an ex vivo model in which PV can persistently infect primary cultures of human fetal brain cells. Two mutations involving capsid residues 142 of VP2 and 95 of VP1 were repeatedly selected during the persistent infections. These residues are located in capsid regions known to be involved in interactions between PV and its receptor. During the first week after infection, viral antigens were found in cells of both the neuronal and glial lineages. In contrast, 2 weeks after infection, viral antigens were detected almost exclusively in cells of the neuronal lineage. They were detected predominantly in cells expressing a marker of early commitment to the neuronal lineage, MAP-5, particularly in neuroblasts. Viral antigens were also found in immature progenitors expressing a neuroepithelium marker, nestin, and in cells expressing a marker of postmitotic neurons, MAP-2. The presence of viral antigens in postmitotic neurons suggests that PV can persist in neurons of patients who have survived poliomyelitis.

Pathogenetic mechanisms of post-polio syndrome: morphological, electrophysiological, virological, and immunological correlations

To understand the mechanism of post-poliomyelitis muscular atrophy (PPMA) and the post-polio syndrome (PPS) in general, we performed the following studies: (1) histopathology in spinal cord sections from patients who died 9 days to 44 years after acute paralytic poliomyelitis; (2) enzyme histochemistry, immunocytochemistry (for lymphocyte subsets, MHC antigens and N-CAM) and polymerase chain reaction (PCR) for poliovirus RNA in the muscle biopsies from symptomatic or asymptomatic muscles of post-polio patients; (3) determination of lymphocyte subsets and circulating IgG or IgM antibodies against GM1 and poliovirus; (4) virological studies in the spinal fluid for oligoclonal bands and search for poliovirus genome with PCR; (5) electrophysiological studies including single fiber EMG, fiber density and macro-EMG; and (6) [31P] exercise MRS spectroscopy on previously affected muscles to search for a metabolic correlate of fatigue. These studies concluded that in PPS a continuing dysfunction is present in the spinal cord motor neurons, resulting in ongoing muscle denervation and reinnervation first evident at the axonal branch points. Symptoms are related to attrition of the oversprouting motor neurons which after a period of time cannot support all their axonal sprouts, resulting in failure of re-reinnervation. In some patients with PPS there is also an ongoing immune activation and presence of defective viral particles in the spinal fluid. However, their role in the pathogenesis of PPS is presently unknown.

How to design a therapeutic study in patients with the post-polio syndrome. Methodological concerns and status of present therapies

The innervation of muscles in patients with the post-polio syndrome (PPS) may differ from limb to limb or even within the same limb because of the segmental nature of the initial involvement and the varying degree of subsequent recovery. Consequently, the compensatory effort of the neighboring muscles varies even in the same limb. Clinicohistological studies have confirmed that in PPS the various muscle groups differ according to whether they were affected during the acute polio and have recovered (partially or completely), or whether they were clinically spared during the original disease, in spite of subclinical involvement. Because the impact of the late effects of polio is also variable in these muscle groups, the effect of therapies may be different not only from patient to patient and from limb to limb, but also from muscle to muscle within the same limb. These variables require careful statistical determination of the sample size at the design of a trial. Another problematic issue in the therapy of PPS is to define the end point of therapy. The two disabling PPS symptoms, excessive fatigue and new muscle weakness, can coexist. An experimental therapeutic design must focus separately on the fatigue, using validated fatigue scales, and on muscle weakness, using quantitative muscle testing. Another methodological concern is the placebo-controlled design. Patients with PPS, even those without depression, can be prone to a placebo effect; hence the need for controlled trials. Finally, the length of a trial remains unresolved because of the slow and unpredictable progression of PPS that varies from patient to patient. Until the natural history of PPS is defined, therapies aimed at arresting disease progression are not reliable.

Detection of poliovirus antibodies and poliovirus genome in patients with the post-polio syndrome

To investigate the role of poliovirus (PV) infection in the development of the post-polio syndrome (PPS), we studied the serum, spinal fluid, peripheral blood lymphocytes, and muscle from 47 patients with PPS. We found high titers of IgM PV antibodies (up to 1:250) in the serum of 6 patients, compared to very low titers (less than 1:50) in normal subjects or disease controls. By polymerase chain reaction, using primers of the replicase PV gene, we amplified PV sequences in the peripheral blood lymphocytes in 7 of 37 patients and in the CSF in 4 of 40 patients, but in none of the controls. Sequencing of the amplified product confirmed that it belonged to PV type 1 with a 99.3% homology. We conclude that some patients with PPS have in the serum high titers of IgM anti-PV antibodies, implying an ongoing antibody response to a viral antigen. The presence of PV-RNA in the CSF or lymphocytes suggests possible persistence of mutated virus or defective PV particles. The significance of these findings in the pathogenesis of PPS remains to be determined.

The post-polio syndrome as an evolved clinical entity. Definition and clinical description

Post-polio syndrome (PPS) refers to the new neuromuscular symptoms that occur at least 15 years after stability in patients with prior acute paralytic polio-myelitis. They include: (1) new muscle weakness and atrophy in the limbs, the bulbar or the respiratory muscles [post-poliomyelitis muscular atrophy (PPMA)] and (2) excessive muscle fatigue and diminished physical endurance. PPS is a clinical diagnosis that requires exclusion of all other medical, neurological, orthopedic or psychiatric diseases that could explain the cause of the new symptoms. Routine electromyography is useful to confirm chronic and ongoing denervation and exclude neuropathies. Muscle biopsy, single fiber electromyography (EMG), macro-EMG, serum antibody titers to polio virus, and spinal fluid studies are very useful research tools but they are rarely needed to establish the clinical diagnosis. PPS is a slowly progressive phenomenon with periods of stability that vary from 3 to 10 years. Current evidence indicates that PPS is the evolution of a subclinically ongoing motor neuron dysfunction that begins after the time of the acute polio. It is clinically manifested as PPS when the well-compensated reinnervating process crosses a critical threshold beyond which the remaining motor neurons cannot maintain the innervation to all the muscle fibers within their motor unit territory.

Rapid cell variation can determine the establishment of a persistent viral infection

Evidence for a mechanism of initiation of viral persistence in which the cell, and not the virus, plays a critical role has been obtained using the important animal pathogen foot-and-mouth disease virus (FMDV). We have developed a virulence assay consisting of quantification of the ability of virus to kill cells and of cells to divide in the presence of virus and to initiate a carrier state. Cells were cured of FMDV at early times following a cytolytic infection of BHK-21 monolayers with FMDV. When cured cells were subjected to the virulence assay they showed an increased ability to survive a second infection by FMDV but not by other RNA viruses. This altered phenotype was maintained as a stable genetic trait. When the virus present in such early surviving cells was used to infect BHK-21 cells, it proved to be as virulent as the initial cytolytic FMDV and, furthermore, its ability to kill BHK-21 cells increased upon replication in the surviving cells. Both the level of genetic heterogeneity and the rate of evolution of FMDV were similar to those previously documented during acute and persistent FMDV infections. The results suggest that, in contrast to most other viral systems, the critical element in the establishment of a persistent infection of BHK-21 cells with FMDV is the ability of the host cells to vary genetically and phenotypically, which promotes selection of cells with increased resistance to virus. The possible relevance of this mechanism to viral persistence in vivo is discussed.

Precise missense and silent point mutations are fixed in the genomes of poliovirus mutants from persistently infected cells

Poliovirus mutants selected in persistently infected human neuroblastoma cells have a modified cell tropism and can establish a secondary persistent infection in nonneural cells, such as HEp-2c cells. Nucleotide sequence analysis revealed that the genome of a persistent mutant, S11, differed from that of the parental lytic Sabin 1 poliovirus strain by 31 point mutations. Three mutations occurred in the noncoding regions. The other mutations resulted in 12 amino acid substitutions; 1 substitution occurred in a nonstructural protein (3A), while the other 11 substitutions were clustered in the capsid proteins VP2 and VP1. The same missense mutations, as well as many of the silent mutations that we observed in mutant S11, also accumulated in the genome of two other persistent viruses isolated from independent infections. This finding indicates that both missense and silent mutations are selected during the persistent infection of neuroblastoma cells and suggests that the secondary structure of RNA in the coding region may play a role in viral infection.

The postpolio syndrome: no evidence for poliovirus persistence

To investigate the possibility of poliovirus persistence in patients with the postpolio syndrome, we examined skeletal muscle biopsy specimens, cerebrospinal fluid specimens, and sera for the presence of poliovirus RNA by the polymerase chain reaction, and for IgM antibodies by a poliovirus type-specific IgM antibody-capture enzyme-linked immunosorbent assay. In none of these specimens was poliovirus RNA or a poliovirus type-specific IgM response detected. These results argue against the hypothesis that poliovirus persists in patients with the postpolio syndrome and plays a role in the pathogenesis of the postpolio syndrome.

Potential role of viruses in neurodegeneration

Viruses have the capacity to induce alterations and degenerations of neurons by different direct and indirect mechanisms. In the review, we have focused on some examples that may provide new avenues for treatment or altering the course of infections, i.e., antibodies to fusogenic virus membrane proteins, drugs that interfere with lipid metabolism, calcium channel blockers, immunoregulatory molecules, and, and inhibitors of excitotoxic amino acids. Owing to their selectivity in attack on regions of nervous tissue, governed by viral factors and by routes of invasion, viral receptors or metabolic machineries of infected cells, certain viral infections show similarities in distribution of their resulting lesions in the nervous system to that of the common human neurodegenerative diseases (namely, motor neurons disease, Parkinson's disease, and Alzheimer's disease). However, it should be emphasized that no infectious agent has as yet provided a complete animal model for any of these diseases, nor has any infectious agent been linked to them from observations on clinical or postmortem materials.

Persistent poliovirus infection: establishment and maintenance involve distinct mechanisms

Mutants of poliovirus (PV) with highly modified biological properties can be selected in vitro in cells of neural origin. Mutations accumulate in the genome of type 1 PV strains selected in human neuroblastoma cells, modifying cell specificity and conferring to the virus the ability to persist in such nonneural cells as HEp-2c (Pelletier et al., Virology 180, 729 1991). With this cell system, we have both parent lytic strains and persistent PV mutants; these were used to study the mechanisms of the establishment and maintenance of the persistent infection. We found that a persistent infection was established when the lytic potential of the virus was reduced; this involved both an early and a late event of the virus cycle for the type 1 mutants. In contrast, maintenance of the infection did not correlate with the reduced lytic potential of the viruses, but rather with the selection of mutant cell populations of various phenotypes. Two cell lines, representative of two phenotypes, were studied in greater detail. In the first one, HEp-S32 (cl7), the PV receptor was not detected by cytofluorometry and viral genomes were detected by in situ hybridization in 2% of the cells. In the second cell line, HEp-S31 (cl18), 97% of the cells expressed the PV receptor, viral genomes were detected in 9-10% of the cells, and viral antigens in 5-10% of the cells. With this cell line, the cure of the culture or, alternatively, the lysis of the majority of cells, could be induced under specific culture conditions. We propose a model involving an equilibrium between an abortive and a lytic infection to explain the properties of cells persistently infected with PV.

Late effects of polio: critical review of the literature on neuromuscular function

Many individuals who have had poliomyelitis are now complaining of several new problems attributed to their former illness including muscle atrophy; fatigue; progressive weakness; and muscle, back, and joint pain. This paper critically examines the literature regarding the neuromuscular effects of poliomyelitis. Weakness resulting from poliomyelitis was due to destruction of anterior horn cells. After the illness, muscle strength was partially recovered as a result of several physiologic adaptive mechanisms including terminal sprouting and reinnervation, myofiber hypertrophy, and, possibly, myofiber type transformation. Several pathophysiologic and functional etiologies have been proposed for late neuromuscular deterioration, but none has been proven. In fact, to date, there is no objective evidence documenting progressive loss of strength in polio survivors. Studies attempting to differentiate polio survivors with and without symptoms of deterioration have resulted in conflicting results; however, it appears reasonable to conclude that symptomatic postpolio subjects had a more severe illness with greater loss of neuromuscular function. Exercise may be helpful for many postpolio patients, but the prescription must be tailored to the individual to avoid problems of overuse or excessive fatigue.

Intrathecal immune response in patients with the post-polio syndrome

BACKGROUND

The syndrome of progressive muscular atrophy decades after acute paralytic poliomyelitis (post-polio syndrome) is not well understood. The theory that physiologic changes and aging cause the new weakness does not explain the immunologic abnormalities reported in some patients. An alternative explanation is persistent or recurrent poliovirus infection.

METHODS

We assessed the intrathecal antibody response to poliovirus and intrathecal production of interleukin-2 and soluble interleukin-2 receptors in 36 patients with the post-polio syndrome and 67 controls (including 13 who had had poliomyelitis but had no new symptoms and 18 with amyotrophic lateral sclerosis). Intrathecal antibody responses to measles, mumps, herpes simplex, and varicella zoster viruses were also determined.

RESULTS

Oligoclonal IgM bands specific to poliovirus were detected in the cerebrospinal fluid of 21 of the 36 patients with the post-polio syndrome (58 percent) but in none of the control group (P less than 0.0001). In quantitative studies there was evidence of increased intrathecal synthesis of IgM antibodies to poliovirus only among the patients with the post-polio syndrome; there was no increased synthesis of IgM to measles, mumps, herpes simplex, or varicella zoster viruses. The patients with post-polio syndrome had significantly higher mean (+/- SD) (cerebrospinal fluid levels of interleukin-2 and soluble interleukin-2 receptors than the controls (8.1 +/- 5.3 vs. 1.4 +/- 0.8 U per milliliter and 159.6 +/- 102.9 vs. 10.7 +/- 6.2 U per milliliter, respectively). The intrathecal synthesis of IgM antibodies to poliovirus correlated with the cerebrospinal fluid concentrations of interleukin-2 (P less than 0.0005) and soluble interleukin-2 receptors (P less than 0.001).

CONCLUSIONS

An intrathecal immune response against poliovirus is present in many patients with the post-polio syndrome. In some of these patients the recrudescence of muscle weakness may be caused by persistent or recurrent infection of neural cells with the poliovirus.

Dysphagia in patients with the post-polio syndrome

BACKGROUND AND METHODS

Dysphagia may develop in some patients many years after an attack of acute paralytic poliomyelitis. To identify clinical or subclinical signs of oropharyngeal dysfunction, we examined 32 patients (mean age, 48.9 years) with the post-polio syndrome (defined by new weakness in the limbs). Of the 32 patients, 14 had symptoms of new swallowing difficulties, and 18 were asymptomatic in this respect; 12 had a history of bulbar involvement during acute poliomyelitis. Swallowing function was assessed objectively by ultrasonography, videofluoroscopy, and an oral motor index score for 10 components of oral function.

RESULTS

All but 1 of the 32 patients, regardless of whether they had new symptoms or previous bulbar involvement, had some abnormality on detailed testing of oropharyngeal function; only 2 patients had any signs of aspiration. The mean oral motor index score (a quantitative measure of oral sensorimotor function) in the patients was higher than that in age-matched normal subjects (P less than 0.001). Videofluoroscopy showed abnormalities of varying severity, including unilateral bolus transport through the pharynx, pooling in the valleculae or pyriform sinuses, delayed pharyngeal constriction, and impaired tongue movements. On ultrasonography, the mean (+/- SD) duration of wet swallows was significantly longer in the symptomatic patients than in the asymptomatic patients (2.67 +/- 0.70 vs. 1.65 +/- 0.42 seconds). The four patients who were reexamined two years later had objective signs of worsening oropharyngeal function and corresponding new symptoms.

CONCLUSIONS

In patients with the post-polio syndrome, the bulbar muscles often have clinical or subclinical signs of dysfunction. These abnormalities suggest that in bulbar neurons there is a slowly progressive deterioration similar to that in the muscles of the limbs.

Creatine kinase and fibrillation potentials in patients with late sequelae of polio

The incidence of an elevated creatine kinase (CK) in a group of polio patients with delayed weakness (15/29) did not differ from polio patients without delayed weakness (9/31) or others with amyotrophic lateral sclerosis (ALS; 10/21). Mean CK in polio patients without delayed weakness (151 IU/L) was lower than the CK in those with delayed weakness (270 IU/L) or ALS (224 IU/L) (P less than 0.05). An elevated CK in polio patients with delayed weakness did not correlate with new or residual weakness. These findings suggest that muscle overuse is either not important or inadequately measured by CK. Widely distributed fibrillations were associated with an elevated CK for all polio patients combined (P less than 0.01). Fibrillations occurred in more muscles of polio patients with delayed weakness (P less than 0.01) and implies that late denervation may play a role in the development of new weakness in some polio patients.

Persistent poliovirus infection of human neuroblastoma cells

Two human neuroblastoma cell lines were persistently infected with poliovirus strains of all three serotypes. In persistently infected IMR-32 cells, which were studied in greatest detail, viral antigens were present in most cells, and over a 9-month period virions were found in the medium at high titers. Persistently infected cells were resistant to superinfection by Sabin 1, 2, and 3 poliovirus but sensitive to coxsackievirus B3. The viruses recovered from persistently infected cells were studied for conservation of epitopes, host cell specificity, and temperature resistance phenotype. The antigenic site 1 carried by the major capsid protein VP1 was modified on the persistent viruses of all three serotypes. This was confirmed for one virus by sequencing the corresponding genomic region in which two mutations were detected. The titers of persistent viruses were 1-3 log10 units higher on IMR-32 cells than on nonneuronal HEp-2 cells, while parental viruses had similar titers on both lines. When thermosensitive viruses were used to initiate the infection, the persistent viruses were found to be thermoresistant at 39 degrees C. Together the results indicate that the persistent infection correlated with the selection of highly mutated viral strains. Poliovirus-infected neuroblastoma cell lines thus constitute an in vitro model of chronic viral infections, which are increasingly implicated in human neural diseases.