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Post-Polio Syndrome: Pathophysiology and Clinical Management
Anne Carrington Gawne and Lauro S. Halstead

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VI. CLARIFICATION OF NOMENCLATURE.

There is disagreement about the most appropriate names or diagnostic labels to describe post-polio patients with new health problems. A number of terms have been proposed, including postpolio syndrome (PPS), post-polio muscular atrophy (PPMA), late effects of polio, and postpolio sequelae. One reason for a lack of consensus is that previously these terms lacked specific diagnostic criteria. This is due to the absence of any pathognomonic tests and our incomplete understanding of the underlying pathophysiology of the presenting complaints. Another reason no single term is suitable for all individuals is that there may be one, two, or more pathologic processes present at any one time producing similar, overlapping symptoms. Separating out the origin of each symptom may not only be impractical but impossible, which gives rise to the need for a more general and less precise diagnostic term. Recently, an attempt was made to be more specific, and these terms have been defined more clearly.

PPMA refers to the clinical and pathological features seen in muscles of post-polio patients who are developing new weakness and atrophy in muscles both affected and apparently unaffected by the polio virus previously. Specifically, there is documented evidence of neuromuscular deterioration with muscle biopsy showing evidence of active denervation in the form of scattered angulated fibers.[36] Mulder first proposed the following criteria for the late progression of weakness in polio survivors in 1972: (1) a credible history of polio, (2) partial recovery of function, (3) a minimum of 10 years of stabilization, and (4) the subsequent development of progressive muscle weakness.[9]

In contrast to PPMA, PPS is a more heterogeneous term and therefore more practical in the typical clinical setting. However, it should not be used indiscriminately for every person with a history of paralytic polio with a new complaint. Criteria for making this diagnosis are outlined in Table 2.[72]

TABLE 2. Criteria for the Diagnosis of Post-Polio Syndrome.
A prior episode of paralytic polio confirmed by history, physical exam, and typical findings on EMG.
Standard EMG evaluation demonstrates changes consistent with prior AHCD: increased amplitude and duration of motor unit action potentials, an increased percentage of polyphasic potentials and, in weak muscles, a decrease in the number of motor units on maximum recruitment; fibrillations and sharp waves may or may not be present.
A period of neurologic recovery followed by an extended interval of neurological and functional stability preceding the onset of new problems; the interval of neurologic and functional stability usually lasts 20 or more years.
The gradual or abrupt onset of new neurogenic, nondisuse weakness in previously affected and/or unaffected muscles; this may or may not be accompanied by other new health problems such as excessive fatigue, muscle pain, joint pain, decreased endurance, decreased function, and atrophy.
Exclusion of medical, orthopedic, and neurologic conditions that might cause the health problems listed above.

The first criterion is a documented history of polio. The diagnosis of paralytic polio usually can be confirmed by examining, whenever possible, the original medical records; eliciting a credible history of an acute, febrile illness producing motor but no sensory loss; noting whether other members of the patient’s family or neighbors had a similar illness; and by observing certain features during physical examination. One very characteristic feature is the presence of focal, asymmetric weakness, and/or atrophy on examination.

The second criterion is a characteristic pattern on EMG. The changes on routine EMG compatible with prior polio include large polyphasic motor unit action potentials (MUAPs) and a decrease in the number of motor units on maximum recruitment in weak muscles. Occasionally, fibrillations are present. These are discussed in detail later in this article.

The third criterion is a characteristic pattern of recovery. In patients with late complications of polio, the pattern of events from onset of polio to onset of new problems is so characteristic that when it is absent the diagnosis should be seriously questioned. The pattern generally consists of three stages, as shown in Figure 9: (1) paralytic polio in childhood or later in life, (2) partial to fairly complete neurologic and functional recovery, (3) a period of functional and neurologic stability lasting many years, and (4) the onset of new health problems.[72]

Figure 9
FIGURE 9. Natural history data from post-polio clinic in Houston, Texas. A = birth; B = onset of polio; C = maximum recovery; D = onset of new health problems; E = time of evaluation; F = death. (Ref. 72.)

The fourth criterion is the onset of new neurogenic, non-disuse weakness that may come on either gradually or abruptly. New neurogenic weakness is essential for making the diagnosis of PPS and presumably reflects new or continuing dysfunction of previously injured motor units. Often this new weakness is accompanied by one or more of the other new health problems listed in Table 2. Although the distinction is not always readily apparent, new neurogenic weakness, in contrast to disuse weakness, can frequently be inferred by the onset of diminished function despite maintaining the usual level and intensity of activity.

And, finally, the fifth criterion is the exclusion of other conditions that might cause the weakness and other health problems listed in Table 2. In addition to distinguishing between disuse and neurogenic weakness, there are several other dilemmas in making the diagnosis of PPS. First, the symptoms are frequently so general that ruling out all possible causes is not practical and can be prohibitively expensive, and, second, co-existing medical, orthopedic, and/or neurologic conditions may be present that can produce a similar set of overlapping signs and symptoms. As indicated in Figure 8, once a problem such as weakness occurs -- regardless of the underlying etiology -- it may initiate a chain reaction of other complications that makes the original problem impossible to identify.

This fifth criterion is often the most difficult to establish. A history of paralytic poliomyelitis does not exempt anyone from getting the chronic illnesses, diseases, or psychiatric disturbances that afflict the general population. When medical, orthopedic, or neurologic conditions coexist with post-polio problems, a similar set of overlapping signs and symptoms may occur. Compression neuropathies, radiculopathies, degenerative arthritis, disc disease, obesity, anemia, diabetes, thyroid disease, and depression are some common examples. Nevertheless, because non-disuse weakness is such an important indicator of PPS, and different etiologies dictate very different management strategies, every attempt should be made to differentiate post-polio weakness from other possible causes.

The terms "the late effects of polio", or "post-polio sequelae" are less specific, and refer to the myriad of new symptoms that patients with a history of polio may experience, regardless if there is evidence of actual new motor unit dysfunction. These symptoms: (1) can be attributed directly to damage caused by the poliovirus, such as cold intolerance, or musculoskeletal imbalance; (2) are thought to be related to the body’s failure to maintain the level of recovery that was achieved following the infection such as new weakness; or (3) result from a secondary trauma, such as the development of carpal tunnel syndrome (CTS) after years of crutch walking.[73] As new information becomes available about the underlying mechanism(s) that produce late onset complications, these criteria will undoubtedly change and new terminology be developed to fit our improved understanding.

Because diagnostic criteria remain nonspecific and pathognomonic tests unavailable, a consistent diagnostic name has not yet been established for new health problems associated with former polio. Indeed, several pathologic processes may interact at any given time to produce similar, overlapping symptoms. The use of a general rather than a precise diagnostic term takes into account the impossibility of determining a distinct origin for each new symptom. The diagnosis "PPS" should be reserved for those patients whose symptomatology indicates motor unit dysfunction with variable musculoskeletal overuse.

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Document preparation: Chris Salter, Original Think-tank, Cornwall, United Kingdom.
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Created: 5th June 2000
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