JULIE K. SILVER, MD
Medical Director, Spaulding-Framingham Outpatient
Center, Framingham, Mass; Assistant professor,
Department of Physical Medicine and Rehabilitation,
Harvard Medical School, Boston, Mass

DOROTHY D. AIELLO, PT
Senior physical therapist, Spaulding-Framingham
Outpatient Center, Framingham, Mass

ABSTRACT
Decades after recovery from polio, many patients develop new muscle weakness and other symptoms that can lead to increased debility. Treatment is aimed at the most prominent symptoms. Medications may help, as well as physical therapy and a carefully paced exercise program. Screening for osteopenia and osteoporosis is recommended.

KEY POINTS
Postpolio syndrome affects an estimated 60% of “paralytic” polio survivors, plus unknown numbers of patients who had subclinical polio.

Postpolio syndrome is a diagnosis of exclusion. Symptoms are related to new muscle weakness and may include muscle atrophy, myalgias, fatigue, and problems with swallowing and breathing.

No drugs specifically address postpolio syndrome.Pyridostigmine has had mixed results for treating weakness and fatigue, as have methylphenidate and bromocriptine. Modafinil may be helpful for fatigue. Nonsteroidal anti-inflammatory drugs are used to treat pain.

Rehabilitation professionals who have expertise in treating polio survivors can be valuable resources in preserving function and preventing deconditioning.

WHEN A POLIO SURVIVOR presents with nonspecific symptoms such as weakness and fatigue, how do you determine whether they are due to postpolio syndrome or to an unrelated problem?

Postpolio syndrome is a neurologic disorder defined by a collection of symptoms occurring decades after a patient has recovered from an initial infection with the poliovirus. New muscle weakness is the hallmark, but breathing or swallowing problems, fatigue, myalgias, and cold intolerance are frequently also present.

In this review, we discuss the criteria for diagnosing postpolio syndrome, guidelines for ruling out other conditions, and treatment strategies to optimize function in postpolio patients.

1 MILLION POLIO SURVIVORS

There are probably at least 1 million polio survivors in the United States, though not all have residual effects. Worldwide, there are millions more. Polio eradication is ongoing, and it is hoped that new cases will be completely eliminated over the next few years.

ACUTE POLIOMYELITIS MAY BE SUBCLINICAL

Historically and even recently, acute poliomyelitis has been thought of as having distinct presentations:

Abortive polio, which presents as a minor illness of fever, malaise, sore throat, anorexia, myalgias, and headache

Nonparalytic polio, which presents as aseptic meningitis

Paralytic polio, which presents as severe back, neck, and muscle pain, with the rapid or gradual development of paralysis.1

In fact, however, the acute viral illness is probably more of a spectrum, in which there are subclinical cases of paralysis that in the past would have been classified as nonparalytic.2 This concept is important because although most patients who are at risk for postpolio syndrome had well-recognized “paralytic” polio, others who were never diagnosed with polio or were thought to have had “nonparalytic” polio may also be at risk for postpolio syndrome.

An estimated 60% of “paralytic” polio survivors are affected by postpolio syndrome.3 The prevalence in those who had subclinical illness is unknown.

WHAT CAUSES THE LATE SYMPTOMS?

Postpolio syndrome occurs in polio survivors who had injury to their central nervous system, generally the anterior horn cells in the spinal cord, during the initial infection. The cause of the late symptoms is not well understood but is believed to involve attrition of motor neurons during aging.4 Other theories abound, however, and the etiology is likely multifactorial.

When motor neurons are lost in acute polio, the surviving motor neurons sprout collateral fibers that reinnervate the denervated muscle fibers (FIGURE 1). The resulting motor units are larger than normal, and there are fewer of them than before. Therefore, the burden on each of these remaining motor neurons is higher than under normal conditions.

With age, we all gradually lose some motor neurons.5 Polio survivors may be more affected by this loss of motor neurons because they have fewer to begin with.

Another theory is that insufficient levels of acetylcholine are released at the neuromuscular junction, resulting in diminished muscle contraction.5

Maselli et al6 noted reduced amplitudes of miniature end plate potentials and structural abnormalities of the neuromuscular junction, such as reduced diameter of nerve terminals, but these changes were not noted in all postpolio syndrome patients.

Some have found ongoing immune activation and defective viral particles in the spinal fluid,7 although the significance of these is unclear.

General fatigue may also have a central cause an abnormality in the reticular activating system in the brain that occurred during the acute polio episode.5,7

HALLMARK IS NEW WEAKNESS

The hallmark symptom of postpolio syndrome is new weakness, which may occur in muscles known to be previously affected or in muscles that were thought to be normal.3 The patient may report difficulty with walking or lifting items, falls, needing more assistance with transfers (eg, moving from the bed or commode to the wheelchair), and being less able to do functional tasks. The weakness characteristically worsens with increased activity and is most pronounced at the end of the day.

Symptoms may also include dyspnea on exertion due to respiratory muscle weakness, other breathing or swallowing problems, pain (myalgias), cold intolerance, and unaccustomed fatigue. New muscle atrophy may also be present.8
Pain can be due to factors related to the history of polio, but which are not classifiable as postpolio syndrome. For example, a patient may present with left leg paralysis due to the initial polio and report increased limping and pain in the right hip (i.e., the “good” leg). The new symptoms may be due to osteoarthritis of the hip, which is more likely to occur in a polio survivor without good muscular support around the hip and after years of additional wear and tear.

Postpolio muscle pain classically occurs in the muscles rather than in the joints. The pain is often described as aching, cramping, burning, or a “tired” feeling. It frequently occurs at night or after the person has been very active.8
Numbness or paresthesias are not typical symptoms of postpolio syndrome.