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

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IX. MORPHOLOGIC FEATURES.

Dalakas et al. evaluated a population of 27 post-polio patients and documented new weakness over an 8-year period.[24] Biopsy findings at follow-up included changes in cell morphology, fiber type grouping, small angulated fibers, and hypertrophy of muscles that were less affected. He then separated morphologic findings according to the severity of involvement (or presumed involvement) of polio. These muscles were placed into one of four subgroups. We briefly summarize the characteristics of each of these groups.

Subgroup I included muscles originally affected, but partially recovered, with subsequent new weakness. These muscles showed a combination of myopathic features, with new and old neurogenic changes. The myopathic features included increased connective tissue, occasional necrotic/phagocytosed fibers, variations of fiber size with big and small but rounded fibers, fiber splitting and an abundance of internal nuclei. The old neurogenic changes included fiber type grouping, groups of small fibers, and small angulated fibers. New neurogenic changes seen included small scattered esterase-positive angulated fibers.

Subgroup II were those muscles originally affected but fully recovered, with new weakness. These showed evidence of extensive reinnervation with fiber type grouping consisting of very large groups of up to 170 normal size fibers and variable small scattered angulated fibers.

Subgroup III were those muscles originally clinically spared with new weakness. These muscles like those in group II showed evidence of chronic enervation/reinnervation with large fiber type grouping and occasional angulated atrophic fibers. Contrary to group II, hypertrophic fibers, internal nuclei, and fiber splitting were rare. Only minimal perivascular inflammation was noted.

Subgroup IV were muscles that were asymptomatic: either apparently unaffected or unaffected with subsequent improvement. These muscles showed fiber type grouping but no small angulated fibers or evidence of inflammation.

Grimby and Einnarsson have demonstrated that morphologic changes seen in muscles of patients with PPS weakness include an increase in fiber area with hypertrophy and an increase percentage of type I fibers. These researchers documented in some polio survivors the fiber area of type I and type IIA myofibers on the average are twice the area seen in control subjects. They also demonstrated there is a fiber type transformation from type II (fast twitch, glycolytic) fibers to type I (slow twitch, oxidative) fibers based on these findings. They suggest that excessive use of remaining muscle fibers leads to hypertrophy, and that this is most prominent in the weakest muscles.[25,28,88] Borg also documented an increased percentage in type I fibers. In addition, internal nuclei and fiber splitting were prominent findings.[89]

In summary, in severely involved muscle myopathic morphologic features include evidence of inflammation and increased connective tissue. Muscles with new enervation may show small angulated fibers, internal nuclei, and fiber splitting. In muscles with reinnervation, large fibertype grouping, fiber-type transformation, and hypertrophy may occur. All of these studies demonstrate the unpredictable nature and wide variability with which polio affects the muscles. No two persons, or even two muscles within the same person, may be affected equally. Because of this, no two people should be treated quite the same. Thus lies the challenge in treating the person with PPS.

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Created: 5th June 2000
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