Lincolnshire Post-Polio Library - A Service of The Lincolnshire Post-Polio Network
The late effects of Polio Information for Health Care Providers
Charlotte Leboeuf

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Some of the recent concepts of the causes of the late effects of polio (LEOP) are summarized below:


It is well established that residual polio is a cause of functional deterioration in many people who have previously had polio. Some clinicians are therefore skeptical about the presence of a new distinct disease entity, rather considering the "new" symptoms as a logical progression of musculoskeletal abnormalities. It is important to keep in mind that symptoms of LEOP can occur also in people who were mildly affected by polio and who have no, or virtually no, obvious residual symptoms and signs of the disease (1).


Paralytic polio results in a diminished number of motor neurones. It is possible that post-polio people are more vulnerable than others, when further motor neurone depletion occurs with normal ageing. Consequently, some attribute the symptoms of LEOP to ageing.

This hypothesis has been contested, since it has been noted that the onset of "new" symptoms is associated with the length of the interval from the onset of polio rather than with age of the person. New symptoms may, in fact, commence at any age and commonly well before the age of 60, when significant age-related loss of motor neurones ordinarily occurs (2).


Amyotrophic lateral sclerosis (ALS) is a progressive disease, which usually begins between the ages of 40 and 60. The initial symptoms resemble some of those of LEOP (weakness and wasting of extremities and bulbar involvement). Similarities of onset and symptoms have prompted the theory that poliomyelitis may evolve into ALS in later years.

Martyn et al (3) noted a striking similarity in the geographical relation between past notification rates of poliomyelitis and current mortality from motor neurone disease in England and Wales. However, people with ALS were not more likely to have had polio than controls according to two retrospective studies (4,5).

Corticospinal tract degeneration, a prominent aspect of ALS, is rare in poliomyelitis (6,7) and muscle weakness in LEOP is not due to a loss of whole motor neurones, as is the case in ALS (8). Furthermore, there are marked clinical differences. ALS has a rapid, relentless progression whereas the muscle weakness and atrophy of LEOP is benign and much more gradual. ALS is characterized by hyperreflexia and extensor plantar reflexes. Such findings are uncommon following paralytic polio, which usually causes flaccid paralysis and hyporeflexia (9). The present consensus appears to be that the neuro-muscular aspect of LEOP is a separate entity from other motor neurone diseases.


Since some of the new symptoms of LEOP resemble those of acute paralytic poliomyelitis (muscle weakness, respiratory distress, pain), they were thought to be caused by a reactivation of a dormant polio virus. Serological tests failed to identify the virus and there is no evidence that it can remain active in the central nervous system for so long (10).

One investigation of long term polio survivors noted alterations in their immune status, which differed both from normal controls and from people with other neurological diseases (11). Other studies have demonstrated immunoglobulin abnormalities in the cerebro-spinal fluid and peripheral lymphocytes (8,12).

Pezeshkpour and Dalakas (7) examined spinal cords from deceased people with a history of poliomyelitis. They found signs of a mild to moderate perivascular and interparenchymal inflammation and concluded that slow disease activity continues silently for many years in the spinal cord. This is an interesting finding, because polio is conventionally thought to be a self-limiting infection.

Perivascular and interstitial inflammatory cells were detected in fully recovered and originally spared muscles in post-polio people (13). Others have failed to confirm findings of immunological and inflammatory processes (10).


The hypothesis of relative overuse of deficient neuromuscular complexes is at present the most commonly held theory.

Each motor unit is made up of a motor neurone, its axon and all muscle fibres innervated by that axon. Following a polio infection, surviving motor neurones enlarge ("sprout") and become responsible for up to 5-10 times as many individual muscle fibres (14).

It is thought that such hypertrophied post-paralytic motor neurones are vulnerable to overuse fatigue. EMG studies have revealed signs of active focal degeneration (15). In fact, Cashman et al (16) established that extensive re-innervation of previously denervated muscles may be followed by a new phase of denervation.

Since muscle fibres which lack neurological command become inactive, others compensate by excessive overuse.

Such compensating muscles have been noted to adapt by developing a predominance of type 1 muscle fibres with marked hypertrophy (17).

Excessive use of post-polio muscles appears to precede their deterioration. It is important to know that muscles which were thought to be spared from the acute disease or believed to have recovered fully on the basis of manual muscle testing may, in fact, have lost up to 50% of their function (18). Since poliomyelitis is a systemic infection, subclinical involvement is likely to have occurred in many cases. Infected individuals may therefore not have been aware of the full extent of muscle involvement.

Excessive muscle use through walking was detected by Ferry et al (19) in subjects with gait abnormalities caused by residual paralysis of some leg muscles. Post-polio muscles have also been shown to need longer time to recover from activity than normal muscles (20). Reduced capacity of the capillary bed may have a negative effect on endurance activity in post-polio muscles (2).

Weakness of the muscles of the extremities and trunk is but one aspect of LEOP. Similar fatigue may occur in the diaphragm and in muscles supplying the throat and mouth.


Although there is evidence of a mild, slow, focal degenerative process in muscles of subjects who once contracted paralytic polio, no definite clinical, electromyographic (EMG), immunological or muscle biopsy findings have, as yet, been able to distinguish clearly between symptomatic and asymptomatic subjects (7,10,11,17,21). Notably age of onset has not been found to correlate with the presence of symptoms (17,21,22) nor has the psychological profile (21).

Some workers have reported differences between stable and deteriorating groups depending on the severity of initial paralysis (22,23) and the relative subsequent degree of functional recovery (22).

Waring et al. (24) noted almost twice as high serum creatine kinase levels in symptomatic as in asymptomatic post-polio people. This is likely to have occurred due to muscle damage and necrosis. A case of post-polio weakness, fatigue and muscle pain with markedly elevated levels of creatine kinase was documented by Peach (25). Following clinical intervention and resolution of symptoms these levels declined. Lange (10) recorded lower amplitude macro-EMG signals in weakened versus non-weakened post-polio muscles. Further studies are needed to confirm or refute these findings.


Polio appears to have a previously unrecognized, second degenerative phase.

It is reasonable to assume that people who have had polio may fatigue their neuro-muscular system even with seemingly modest levels of activity. The overuse fatigue theory provides not only a possible aetiology of muscle fatigue but also explains how muscles and joints may become strained and painful due to insufficient muscle strength. It also provides a rationale for the prevention and management of LEOP - the concept of energy management. Fortunately, it is possible that the symptoms are reversible.

The presence of immunological and/or inflammatory changes may also explain the complaints of unpredictable, often influenza-like muscle pain, exhaustion and excessive need for rest as well as the slow deterioration of muscle strength.

There are signs of slow deterioration during the late post-convalescent period in most post-polio muscles but for unknown reasons only some people experience symptoms. More research is needed to identify the long-term effects of previous polio infection and, in particular, predictors of symptomatic deterioration. It will also be necessary to compare the development of symptoms with that of an ageing polio-free population.

The variation of symptoms relating to LEOP suggest that individual susceptibility plays a role in the development of the disease and it may have a multifactorial cause.

If the senescence theory is at least partially correct, it is to be expected that, as the post-polio population ages, the incidence of new complaints and/or the severity of dysfunction will increase.


  1. Dalakas MC. New neuromuscular symptoms in patients with old poliomyelitis: A three-year follow-up study. Eur Neurol 1986;25:381-7. [PubMed Abstract]
  2. Grimby G, Einarsson G, Hedberg M, Aniansson A. Muscle adaptive changes in post-polio subjects. Scand J Rehab Med 1989;21:19-26. [PubMed Abstract]
  3. Martyn CN, Barker DJP, Osmond C. Motoneuron disease and past poliomyelitis in England and Wales. Lancet 1988;June 11;1 (8598):1319-22. [PubMed Abstract]
  4. den Hartog Jaeger WA, Hanlo PW, Ansink BJ, Vermeulen MB. Results of a questionnaire in 100 ALS patients and 100 control cases. Clin Neurol Neurosurg 1987;89:37-41. [PubMed Abstract]
  5. Deapen DM, Henderson BE. A case-control study of amyotrophic lateral sclerosis. Am J Epidemiol 1986;123:790-9. [PubMed Abstract]
  6. Fishman PS. Late-convalescent poliomyelitis. Corticospinal tract integrity. Arch Neurol 1987;44:98-100. [PubMed Abstract]
  7. Pezeshkpour GH, Dalakas MC. Long-term changes in the spinal cords of patients with old poliomyelitis. Signs of continuous disease activity. Arch Neurol 1988;45:505-8. [PubMed Abstract]
  8. Dalakas MC, Elder G, Hallat M et al. A long-term folllow up study of patients with post-poliomyelitis neuromuscular symptoms. N Engl J Med 1986;314:959-63. [PubMed Abstract]
  9. Meineri P, Brignolio F, Chio A et al. Post-poliomyelitic motor neuron disease. Clinical aspects and its relation to typical motor neuron disease. Eur Neurol 1988;28:177-80. [PubMed Abstract]
  10. Lange DJ, Smith T, Lovelace RE. Postpolio muscular atrophy. Diagnostic utility of macroelectromyography. Arch Neurol 1989;46:502-6. [PubMed Abstract]
  11. Ginsberg AH, Gale MJ Jr, Rose LM, Clark EA. T-cel alterations in late postpoliomyelitis. Arch Neurol 1989;46:497-501. [PubMed Abstract]
  12. Dalakas MC, Sever JL, Maddan DL et al. Late postpoliomyelitis muscular atrophy: clinical, virologic and immunologic studies. Rev Infect Dis 1984;6 Suppl 2:562-7. [PubMed Abstract]
  13. Dalakas MC. Morphologic changes in the muscles of patients with postpoliomyelitis neuromuscular symptoms. Neurology 1988;38:99-104. [PubMed Abstract]
  14. Wiechers DO. Acute and latent effects of poliomyelitis on the motor unit as revealed by electromyography. Orthopedics 1985;8:870-2. [PubMed Abstract]
  15. Wiechers DO. New concepts of the reinnervated motor unit revealed by vaccine-associated poliomyelitis. Muscle & Nerve 1988;11:356-64. [PubMed Abstract]
  16. Cashman NR, Maselli R, Wollmann RL et al. Late denervation in patients with antecedent paralytic poliomyelitis. N Engl J Med 1987;317:7-12. [PubMed Abstract]
  17. Borg K, Borg J, Edström L, Grimby L. Effects of excessive use of remaining muscle fibers in prior polio and LV lesion. Muscle & Nerve 1988;11:1219-30. [PubMed Abstract]
  18. Perry J, Fleming C. Polio: Long-term problems. Orthopedics 1985;8:877-81. [PubMed Abstract]
  19. Perry J, Barnes G, Gronley JK. The postpolio syndrome. An overuse phenomenon. Clin Orthop 1988;233:145-62. [Lincolnshire Library Full Text]
  20. Agre JC, Rodriguez AA. Neuromuscular function: A comparison of symptomatic polios to asymptomatic polios and controls. Dept. of Rehab. Med., University of Wisconsin Medical School, Madison, Wisconsin 53792 (Presented at the Fifth International Polio and Independent Living Conference, May 31 - June 4, 1989).
  21. Windebank AJ. Conclusions from Omstead County. Polio Network News 1989;5:3-5 (Preliminary report).
  22. Klingman J, Chui H, Corgiat M, Perry J. Functional recovery. A major riskfactor fro the development of postpoliomyelitis muscular dystrophy. Arch Neurol 1988;45:645-7. [PubMed Abstract]
  23. Halstead LS, Wiechers DO, Rossi CD. Late effects of poliomyelitis, national survey. In: Halstead LS, Wiechers DO (eds): Late effects of poliomyelitis. Miami, Symposium Foundation, 1989.
  24. Waring WP, Davidoff G, Werner R. Serum creatine kinase in the post-polio population. Am J Phys Med Rehabil 1989;68:86-90 (abstract). [PubMed Abstract]
  25. Peach PE. Overwork weakness with evidence of muscle damage in a patient with residual paralysis from polio. Arch Phys Med Rehabil 1990;71:248-50. [PubMed Abstract]

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© Copyright The Lincolnshire Post-Polio Network 1997 - 2010.

This document comprises an index, foreword, introduction and seventeen other sections or subdocuments. Permission for printing copies is granted only on the basis that ALL sections are printed in their entirety and kept together as a single document.

Document preparation: Chris Salter, Original Think-tank, Cornwall, United Kingdom.
Created: 7th July 1997
Last modification: 20th January 2010.
Last information content change: 6th June 2000

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