Force assessment in periodic paralysis after electrical muscle stimulation.
OBJECTIVE
To obtain an objective measure of muscle force in periodic paralysis, we studied ankle dorsiflexion torque during induced paralytic attacks in hyperkalemic and hypokalemic patients. SUBJECTS, PATIENTS, AND METHODS: Dorsiflexor torque after peroneal nerve stimulation was recorded during provocative tests on 5 patients with hypokalemic or hyperkalemic disorders and on 2 control subjects (1995-2001). Manual strength assessment was simultaneously performed in a blinded fashion. Standardized provocation procedures were used.


RESULTS
The loss of torque in hyperkalemic patients roughly paralleled the loss of clinically detectable strength, whereas in the hypokalemic patients, pronounced torque loss occurred well before observed clinical effects. No dramatic changes occurred in the control subjects. Torque amplitude decreased more than 70% in all patients during the provocation tests; such decreases were associated with alterations induced in serum potassium concentrations.


CONCLUSIONS
Stimulated torque measurement offers several advantages in characterizing muscle dysfunction in periodic paralysis: (1) it is independent of patient effort; (2) it can show a definitely abnormal response early during provocative maneuvers; and (3) characteristics of muscle contraction can be measured that are unobservable during voluntary contraction. Stimulated torque measurements can characterize phenotypic muscle function in neuromuscular diseases.
Day
John W
JW
Department of Neurology, University of Minnesota School of Medicine, Minneapolis 55455, USA.
Sakamoto
Carl
C
Parry
Gareth J
GJ
Lehmann-Horn
Frank
F
Iaizzo
Paul A
PA
D000293:Adolescent; D000328:Adult; D016022:Case-Control Studies; D018450:Disease Progression; D004558:Electric Stimulation / Q000379:methods*; D005947:Glucose; D006801:Humans; D020514:Hypokalemic Periodic Paralysis / Q000145:classification / Q000150:complications* / Q000175:diagnosis* / Q000235:genetics; D007328:Insulin; D007537:Isometric Contraction; D018908:Muscle Weakness / Q000209:etiology* / Q000503:physiopathology*; D020513:Paralysis, Hyperkalemic Periodic / Q000145:classification / Q000150:complications* / Q000175:diagnosis* / Q000235:genetics; D010543:Peroneal Nerve / Q000503:physiopathology*; D010641:Phenotype; D011189:Potassium Chloride; D016059:Range of Motion, Articular; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted; D016037:Single-Blind Method; D013997:Time Factors; D019415:Torque
D007328:Insulin; D011189:Potassium Chloride; D005947:Glucose