1.2.1

Natural history of poliomyelitis

During the initial phase of the disease, the targets of the disease are the motoneurons of the anterior horn cells of the spinal cord and the brainstem, paralytic poliomyelitis leads to asymmetric muscular paralysis, with varying degrees of severity, reaching its peak in 48 hours and sometimes associated to a respiratory and bulbar affection. After the acute infection, there is a slow and progressive “recovery” phase. One mechanism involved in recovery is nerve terminal sprouting, in which remaining brainstem and spinal cord motor neurons develop new branches, or axonal sprouts. These sprouts can reinnervate orphaned muscle fibers that have been denervated by acute polio infection, restoring the fibers’ capacity to contract and improving strength. Terminal sprouting generate a few significantly enlarged motor neurons identified on electromyography recordings . This mechanism cannot benefit to all denervated fibers, explaining the residual motor sequelae. The recovery phase optimized by physical rehabilitation, leads to a “sequelae-related impairment” stage that can be very different according to individuals.

Aging of the neuromuscular system under chronic denervation:

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  Alteration of the structure of muscular fibers :

  
  
  
  
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    The muscular fibers of the partially denervated and solicited muscles modify their structure: changes were described in the isoform phenotypes of contractile cells associated to the changes in contractile properties of type 1 fibers,

    
    
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    Denervation also leads to metabolic changes: the decrease in production capacity of type 1 muscular fibers obtained from patients with poliomyelitis sequelae was reported and deemed responsible for a greater fatigue compared to healthy muscular fibers;

  
  
  
  
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  The reinnervation mechanism observed at the beginning of the affection does not linger over time and reinnervated motor fibers become unstable on the long term with a progressive loss of their axonal nerve terminals, leading to a size decrease of the giant motor units. Several hypotheses have been reported on this deterioration: Years of intense use of these enlarged motor units adds stress to the neuronal cell body, which then may not be able to maintain the metabolic demands of all the new sprouts, resulting in the slow deterioration of motor units , deterioration of the denervation-reinnervation mechanism at the level of newly formed neuromuscular junctions. This phenomenon seems to be aggravated by an intense muscular activation on the long term ;

  
  
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  Finally, some brought up the hypothesis of the deterioration of the motor cortex’s cortical command, validated by the alteration of the evoked motor potentials after an effort .

These changes lead to a progressive alteration of muscular strength and functional abilities over time in patients with poliomyelitis sequelae. These alterations cannot just be explained by average physiological neuromuscular aging as seen in the general population.

The incidence of this late deterioration is unclear just like its prognostic factors. In order to implement preventive and therapeutic measures, it is essential to comprehend the causes and factors that promote this deterioration . The evolution is not ineluctably ill fated. PPS can be evoked as a diagnosis, once all the other causes have been discarded.

1.3.1

General factors

Weight gain, even a slight weight gain, can greatly contribute to this late functional deterioration. Weight gain usually occurs with aging, decrease in physical activity and menopause in women. Gawne et al. , out of a population of 88 individuals who survived polio as children, reported 25 patients (corresponding to 28,4% of the series) who had a body mass index (BMI) greater than 25 kg/m ² . Obesity itself leads to a decrease in physical activity and thus underused muscles easily fatigued during efforts . Obesity can also cause a loss of gait ability when there is a muscular wasting of the lower limbs: the inability to lock the knee can be responsible for falls for example… Weight gain puts an additional load on all the joints thus promoting the onset of degenerative orthopedic complications.

Some recent studies showed that the prevalence of dyslipidemia – 61,3% out of a population of 88 polio survivors – was higher in this population than in the general population. Associated to being overweight, these metabolic disorders are an additional risk factor for cardiovascular diseases.

Just like weight gain, any intercurrent complications such as the flu or a routine surgical intervention can have unexpected consequences: muscular atrophy correlated to being bedridden has more severe consequences in patients with sequelae of a neuromuscular disease than in the general population.

Finally, physiological aging and the accompanying loss of neurons also participate in these mechanisms of secondary deterioration .

1.3.2

Orthopedic complications

There is a high incidence of tendon diseases in this population . Their prevalence remains unknown. These diseases are fostered by the use of canes or wheelchair . They mostly affect the upper limbs: shoulder (rotator cuff) or elbow (epicondylitis). Immediate proper medical care is essential in order to limit the aggravation of the lesions, the decreased activity and the development of chronic symptoms.

Secondary arthritis affects mostly the lower limbs: knee and hip arthritis. It can also be located on the upper limbs: shoulder arthritis, acromioclavicular arthritis, elbow arthritis… the prevalence of arthritis conditions was studied by Kidd et al. on a series of 283 polio survivors presenting a late-setting functional deterioration: 150 patients, 63% of the total population, had clinical arthritis validated by X-rays on at least one joint. An arthritis aggravation of knee recurvatum is quite common . In fact, knee recurvatum allows some patients to lock their knee while walking to compensate for insufficient quadriceps ( Fig. 1 ). Along the years and commonly with additional weight gain, the knee can become painful (meniscal and cartilage injuries, arthritis) or unstable. Some static disorders of the feet can also be aggravated over time: painful instability, arthritis of the tibiotarsal, talonavicular or tarsometatarsal joints. The difficulties in finding proper footwear can lead to gait disorders.

Knee recurvatum allowing for knee locking during loading to make up for the lack of quadriceps.

Osteoporosis is more common in polio survivors than in the general population mainly at hip level. At hip level, Haziza et al. find a prevalence of 32% in men, 12,5% in premenopausal women and 27% in menopausal women. This osteoporosis, associated to a higher incidence of falls in this population, can be complicated by fractures. These fractures, surgically repaired or not, require a total immobilization, sometimes over a long period of time, thus leading to muscular wasting and muscular deconditioning.

Finally, late-setting spinal cord complications are quite common in polio survivors. There can be isolated lumbar back pain or associated to radicular pain, linked to degenerative dysfunctions: herniated disc, arthritis, tightened lumbar or cervical canal… It can also be due to the aggravation of pre-existing scoliosis or kyphosis ( Fig. 2 ). Degenerative disc pathologies can also appear above or below a spinal arthrodesis operated on during the patient’s adolescence .

Very severe kyphosis and scoliosis spinal deformations at an adult age, causing major back pain and contributing to the onset of restrictive respiratory insufficiency.

1.3.3

Neurological complications

Fatigue is one of the most common symptoms in poliomyelitis sequelae . It is reported for 59 to 89% of patients according to the different studies. This fatigue could be related to an alteration of the function of the neuromuscular junctions developed during the recovery process after the initial polio infection. Some patients also experience central fatigability (decreased attention and concentration and memory loss) due to involvement of various brain structures including the reticular activating system or basal lymph nodes. Most other neurological complications are entrapment syndromes of the upper limbs triggered by the use of canes, wheelchair propulsion or transfers. Their incidence was estimated at 80% of patients according to the team of Tsai et al. based on electrophysiological data. The compression of the median nerve of the carpal tunnel is the most common and affects 62% of patients. The compression of the ulnar nerve in the wrist, on the upper third of the forearm (canes, crutches) or in the elbow with cubital tunnel syndrome (wheelchair arm rests) is less common. These entrapment syndromes of the upper limbs are not specific to polio sequelae and were also described in other patients using canes, crutches or wheelchairs (Spinal cord injury patients…). Radicular affections, sciatica or crural neuralgia for example, can also been seen in case of herniated disc, foraminal stenosis or tightening of the lumbar spinal canal.

It is very rare to see spinal cord affections complicating the major spinal deformities.

1.3.4

Oral, pharyngeal and respiratory complications

A late restrictive respiratory failure is possible , especially in case of an initial respiratory affection. This late failure corresponds to several causes: decrease in respiratory muscles’ strength, aggravation of spinal cord deformities, stiffness of the rib cage, recurrent bronchial and parenchymal infections… The symptoms are often quite difficult to interpret. Shortness of breath during exercise or daytime sleepiness should bring up the diagnosis. A simple exhaustion or acute muscular fatigue can also unveil the beginning of a respiratory insufficiency.

Sleep apnea syndrome (SAS) is statistically more common in polio survivors than in the general population . Its prevalence is higher than 50% in polio survivors with asthenia. In 86% of case, it is an obstructive sleep apnea. The associated symptoms are fatigue and daytime sleepiness. Besides fatigue, morning headaches and daytime sleepiness should be related to SAS, just like snoring or sleep apnea reported by the patient’s family.

Oral and pharyngeal dysfunctions can be seen in some patients . The late onset of swallowing disorders, dysphagia, dysarthria or aphonia is rare but possible .

1.3.5

Sleep disorders

Periodic jolts of the lower limbs and/or restless legs syndrome are more frequent in this population , however, their prevalence remains unknown. Responsible for nighttime awakening, these disorders can also trigger major exhaustion and aggravate muscular fatigability.

1.3.6

Post-poliomyelitis syndrome

PPS is an elimination diagnosis but it is also directly related to the other causes of late-onset deterioration described above, as well as physiological aging disorders. The diagnosis criteria and treatments were described in another article in this review and thus will not be covered in this study.

1.4.1

Comprehensive medical care

A comprehensive medical care is essential, with a good knowledge of the initial pathology and its late-onset consequences. Proper medical follow-up of polio survivors can help implement early on preventive measures and an adequate treatment to avoid the complications listed above: information (on the pathology and its evolution, vaccinations, consequences of the associated complications…), promote a proper diet and healthy lifestyle (weight management, exercise…) screening and treatment of osteoporosis…

These specialized consultations are a good opportunity to explain to patients how to implement “energy conservation” measures in order to preserve their remaining muscular and orthopedic strength : lifestyle changes and reducing workload (respectful of fatigue episodes, daytime sleeping, avoiding specific exhausting activities or injury-prone movements for the shoulders for example), adapting the environment, technical aids to simplify daily life activities…

Orthopedic complications can justify a specialized treatment not directly related to the initial affection: anti-inflammatory drugs, infiltrations of cortisone or hyaluronic acid derivatives, physical rehabilitation, surgery…

1.4.2

Specific medical treatments

Besides the specific PPS treatments that will not be covered here, some molecules have been proposed for the treatment of some symptoms encountered in polio survivors. Some benefited from controlled studies that could not prove their efficacy: Modafinil or Amantadine for fatigue , Coenzyme Q10 or Pyridostigmine for treating muscular weakness, Lamotrigine for pain relief …

The prescription of dopamine agonists for restless legs syndrome has a validated efficacy and has no specific precautions related to a history of poliomyelitis. The prescription of a therapeutic treatment for osteoporosis must be proposed, as primary and secondary prevention. Here also, no specific requirements for polio survivors.

1.4.3

The place of physical rehabilitation

Physical rehabilitation for this late deterioration is very different in its techniques, limits and objectives than the one proposed to the patients at the beginning of their polio infection. It will not be detailed here as it is the theme of an article in this same magazine .

1.4.4

Orthotics and technical aids

The prescription or the renewal of an orthotic device for the lower limbs or orthopedic shoes is a common reason for consulting. For example, leg orthoses for knee locking or anti-recurvatum orthoses, these orthotic devices have greatly benefited from the technical advances of these past 20 years : perfected measurement systems (Computer aided measurement), lighter materials (carbon), increased safety for all pieces (locks…)… The manufacturing technique for orthopedic shoes has also greatly improved and now the shoes are light, discreet and fashionable, without loosing any of their foot support quality.

Technical aids are often quite necessary for this population . This is an ever-growing field. Mobility aids (canes, walker, wheelchairs…) are quite diversified and several different models are available. Home environment aids, just like automobile equipments, require specific advice and need to be specifically adapted for each individual. Physical rehabilitation personnel (physiotherapists and occupational therapists) have an essential role to play in helping patients choose the appropriate technical aids and equipments.

1.4.5

Therapeutic care of respiratory disorders and sleep disorders

Respiratory insufficiency or sleep apnea should be screened out and a specific treatment should be administered . Flu vaccines are highly recommended. Respiratory physical therapy can be indicated (clear a chest obstruction in case of infection, muscle strengthening exercise, keeping up adequate lung volume…). Implementing non-invasive ventilation with an oxygen mask can also be quite useful in certain cases to treat a restrictive respiratory insufficiency or sleep apnea. In some rare cases, an indication for oxygen therapy or tracheotomy must be proposed to the patients.

1.4.6

Place of surgery

Sometimes, orthopedic surgery directly related to polio sequelae can be indicated: late surgery for scoliosis or kyphosis, osteotomy of the femur to create a recurvatum, late surgery to treat foot deformities .

Surgery of the vocal cords can sometimes be necessary when confronted to severe laryngeal dysfunctions , after failure of medical techniques such as speech therapy or botox injections .

Other surgical indications are not specific to polio sequelae and are regularly suggested to these patients: surgical treatment for an entrapment syndrome of the upper limb, surgical treatment for shoulder tendon tear or arthroscopic subacromial decompression (ASD) for shoulder impingement, surgical treatment of herniated disc or tightened spinal lumbar canal… The indications for joint replacement surgery (arthroplasty) are quite rare for polio patients , whether on the upper limbs than on the lower limbs. In fact, the muscular deficit around the joints cannot predict a good outcome for these surgical techniques.

2.2.1

Histoire naturelle de la poliomyélite

À la phase initiale de la maladie, la cible du poliovirus étant les corps cellulaires des motoneurones de la corne antérieure de la moelle ou du tronc cérébral, la poliomyélite antérieure aiguë se manifeste par une paralysie musculaire asymétrique, de sévérité variable, maximale en 48 heures et pouvant s’accompagner d’une atteinte respiratoire et bulbaire. Après l’infection aiguë, s’installe une phase de « récupération » lente et progressive. Cette récupération motrice est rendue possible par le phénomène de ré-innervation des fibres musculaires initialement dénervées par les axones des motoneurones épargnés par le virus et capables de « bourgeonner » (phénomène de « sprouting »), créant des unités motrices géantes identifiables sur les enregistrements électromyographiques . Ce phénomène ne peut cependant pas bénéficier à toutes les fibres dénervées, ce qui explique la persistance de séquelles motrices. La période de récupération, potentialisée par la rééducation, aboutit à une période de « déficiences séquellaires », de distribution et de sévérité très polymorphes.

Vieillissement du système neuromusculaire en condition de dénervation chronique :

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  altérations de la structure des fibres musculaires :

  
  
  
  
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    les fibres musculaires des muscles partiellement dénervés et sollicités modifient leur structure : des modifications d’expression phénotypique des isoformes de protéines contractiles associées à des changements des propriétés contractiles des fibres de type I on été décrites,

    
    
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    la dénervation induit également des modifications métaboliques : la diminution de capacité de production énergétique des fibres de type I de muscles prélevés sur des sujets atteints de séquelles de poliomyélite a été observée et jugée responsable d’une plus grande fatigabilité en comparaison des fibres musculaires saines ;

  
  
  
  
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  le mécanisme de ré-innervation observé au début de l’affection ne se maintient pas dans le temps et les fibres motrices ré-innervées subissent une instabilité à long terme avec perte progressive de leurs terminaisons axonales, qui s’exprime par une diminution de la taille des unités motrices géantes. Diverses hypothèses ont été avancées qui rendent compte de cette dégradation : épuisement métabolique précoce de certains motoneurones , épuisement des phénomènes de dénervation-réinnervation au niveau des jonctions neuromusculaires néoformées. Ce phénomène serait aggravé par une activation musculaire intense et prolongée ;

  
  
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  enfin, l’hypothèse d’une fatigabilité de la commande motrice d’origine corticale, objectivée par l’altération des potentiels évoqués moteurs post-effort, a été avancée .

Ces changements se traduisent par une altération progressive de la force musculaire et des capacités fonctionnelles dans le temps chez les sujets atteints de séquelles de poliomyélite. Ces altérations ne s’expliquent donc pas uniquement par un vieillissement neuromusculaire physiologique tel qu’il est observé dans la population générale.

L’incidence de cette dégradation tardive est mal connue, de même que ses facteurs pronostiques. Le démembrement des causes et des facteurs qui favorisent cette dégradation tardive est indispensable pour mettre en place des mesures préventives et curatives. L’évolution n’est pas inéluctablement défavorable. Le SPP reste un diagnostic d’élimination, une fois que toutes les autres causes ont été éliminées.

2.3.1

Facteurs généraux

Une prise de poids, même minime, peut fortement contribuer à cette dégradation fonctionnelle tardive. La prise de poids est favorisée par l’âge, la diminution d’activité, la ménopause chez la femme. Gawne et al. , sur une population 88 anciens poliomyélitiques, recense 25 patients (soit 28,4 % de la série) présentant un index de masse corporelle supérieur à 25 kg/m ² . L’obésité entraîne elle-même une diminution d’activité qui peut mener à un déconditionnement à l’effort . Elle peut occasionner la perte des capacités de marche lorsque le capital musculaire des membres inférieurs est faible : impossibilité de verrouiller le genou à l’origine de chutes par exemple… Elle occasionne une surcharge de toutes les articulations, favorisant ainsi la survenue de complications orthopédiques dégénératives.

Des travaux récents ont, par ailleurs, montré que la prévalence des dyslipidémies – 61,3 % sur une population de 88 anciens poliomyélitiques – était plus importante dans cette population que dans la population générale. Associées à la surcharge pondérale, ces anomalies métaboliques constituent un facteur de risque supplémentaire de morbidité cardiovasculaire.

Au même titre que la prise de poids, toutes les complications intercurrentes comme une simple grippe ou une intervention chirurgicale de routine peuvent avoir des conséquences inattendues : la fonte musculaire liée à l’alitement a des conséquences beaucoup plus sévères chez un patient porteur de séquelles d’une maladie neuromusculaire que dans la population générale.

Enfin, le vieillissement physiologique et la perte neuronale qui l’accompagne participent de façon importante aux phénomènes de dégradation secondaire .

2.3.2

Complications orthopédiques

Les tendinopathies ont une incidence élevée dans cette population . Leur prévalence n’est pas connue. Elles sont favorisées par l’utilisation des cannes ou du fauteuil roulant . Elles intéressent tout particulièrement les membres supérieurs : tendinopathies de l’épaule (coiffe des rotateurs) ou du coude (épicondylites). Une prise en charge médicale rapide est indispensable afin d’éviter l’aggravation des lésions, la diminution d’activité et la chronicisation des symptômes.

Les arthroses secondaires se voient surtout au niveau des membres inférieurs : gonarthroses , coxarthroses. Elles peuvent également se rencontrer au niveau des membres supérieurs : omarthrose, arthrose acromioclaviculaire, arthrose du coude… La prévalence des manifestations arthrosique a été étudiée par Kidd et al. sur une série de 283 anciens poliomyélitiques présentant une dégradation fonctionnelle tardive : 150 patients, soit 63 % de l’ensemble, présentaient une arthrose clinique et radiologique au niveau d’au moins une articulation.

L’aggravation arthrosique d’un récurvatum de genou est très classique . Le recurvatum du genou permet en effet à certains patients de verrouiller leur genou à la marche en l’absence de quadriceps suffisant ( Fig. 1 ). Au fil des années et souvent à la faveur d’une prise de poids, le genou peut devenir douloureux (souffrance cartilagineuse et méniscale, gonarthrose) ou instable. Certains troubles statiques du pied peuvent également évoluer défavorablement vers des instabilités douloureuses, des arthroses de l’articulation talocrurale, médiotarsienne ou sous-talienne. Les difficultés au chaussage qui en découlent peuvent entraîner un trouble de la marche.

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