Key result
Baseline electromyography abnormalities in clinically normal muscles of polio survivors predicted muscle weakness 2 years later, with sensitivity ranging from 0.67 to 1.00 in the lower limbs.
Why the study?
Post-polio syndrome-induced muscle weakness can develop in limbs considered unaffected by polio, motivating investigation into whether electromyography can predict future weakness in these muscles.
Does baseline electromyography predict future muscle weakness in clinically unaffected muscles of polio survivors?
Cohort (n=77)
No
Does baseline electromyography predict future muscle weakness in clinically unaffected muscles of polio survivors?
EMG abnormalities can predict future muscle weakness in clinically normal muscles of polio survivors, with predictive value varying by muscle group.
May inform muscle-specific monitoring in polio survivors; leaves open prospective validation before clinical adoption.
BACKGROUND: Post-polio syndrome-induced muscle weakness may develop in limbs that have had normal muscle strength and have been considered unaffected by polio. OBJECTIVE: To investigate the utility of electromyography (EMG) for predicting future muscle weakness in clinically unaffected limb muscles of polio survivors. DESIGN: Retrospective study. SETTING: Academic polio clinic. PARTICIPANTS: Polio survivors (N = 77) who underwent EMG between April 2008 and March 2010 and were followed for at least 2 years. MATERIALS AND METHODS: Chart reviews were conducted to extract baseline EMG and manual muscle strength test (MMT) results to investigate the relationship between baseline EMG abnormalities and change in muscle strength over 2 years for various upper and lower limb muscles that control movement in the limb joints. MAIN OUTCOME MEASUREMENTS: Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of EMG findings for prediction of subsequent muscle weakness. RESULTS: EMG data were available for 44 deltoid, 59 biceps brachii, 60 triceps brachii, 59 vastus lateralis, 59 tibialis anterior, and 55 gastrocnemius (medial head) muscles. The percentage of muscles with an initial MMT of grade 5 that developed weakness over 2 years of follow-up was approximately 15% for most muscle types. Sensitivity of EMG to predict subsequent weakness was higher in the lower limbs (0.67-1.00). Specificity was higher in the biceps brachii (0.83). PPV was higher in the biceps brachii (0.50). NPV was higher in the lower limbs (0.89-1.00) but lower in the deltoid (0.75). CONCLUSION: EMG abnormalities were detected in some clinically normal muscles of polio survivors. EMG abnormalities predicted muscle weakness 2 years later, although the strength of this relationship varied depending on the muscle.
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Sawada et al. (2019) conducted a cohort in Polio survivors (n=77). Electromyography (EMG) abnormalities vs. Normal EMG findings was evaluated on Subsequent muscle weakness. Baseline electromyography abnormalities in clinically normal muscles of polio survivors predicted muscle weakness 2 years later, with sensitivity ranging from 0.67 to 1.00 in the lower limbs.
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