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Double‐Step nerve stimulation test for myasthenic block: Sensitization of postactivation exhaustion by ischemia
Author(s) -
Desmedt John E.,
Borenstein Samuel
Publication year - 1977
Publication title -
annals of neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.764
H-Index - 296
eISSN - 1531-8249
pISSN - 0364-5134
DOI - 10.1002/ana.410010105
Subject(s) - medicine , myasthenia gravis , forearm , neuromuscular transmission , stimulation , ulnar nerve , ischemia , anesthesia , paresis , wrist , physical medicine and rehabilitation , cardiology , surgery , elbow
A new, double‐step test is described that increases the yield of diagnostically useful data in patients with localized ocular or bulbar paresis who may have myasthenia gravis. The first step involves a program of supramaximal stimulation of the ulnar nerve at a rate of 3 per second for four minutes while electrical responses are recorded in four muscles of the hand and forearm to detect decrements and postactivation exhaustion. The second step delivers the same program under ischemia and elicits decrements from the subclinically involved muscles that reacted normally to the first step. Control tests in a large number of normal subjects established the conditions that efficiently challenge the muscles with a reduced safety factor for neuromuscular transmission while avoiding false‐positive results. The test involves the hypoxic failure of neurochemical processes. The ulnar flexor muscle of the wrist in athletic normal men was surprisingly more susceptible to ischemic exercise than the other normal muscles. The diagnostic uses of the double‐step test are documented in patients in whom the orbicular muscle of the eye and the proximal limb muscles reacted normally, and the concept of occult myasthenia gravis is discussed.