Table 1.

Peripheral axonal excitability findings in neuromuscular disorders

Disease	Excitability findings			References
	Strength-duration time constant	Recovery cycle	Threshold electrotonus and I/V relationship
Motor neuron disease	Prolonged	Increased superexcitability	Increased TEd and TEh	[6–8, 58, 61, 76]
Kennedy’s disease	Prolonged	Minor changes	Increased hyperpolarizing I/V slope; increased TEd	[116]
Multifocal motor neuropathy	No change	Decreased RRP; increased superexcitability	Increased TEd and TEh; decreased resting I/V slope	[14, 139, 140]
Chronic inflammatory demyelinating polyneuropathy	Reduced	Variability with disease stage—decreased recovery cycle parameters or no changes	Variability with disease stage—increased TEd and TEh or no changes	[140, 142, 144, 145]
Spinal muscular atrophy	Prolonged in severe disease	Increased subexcitability in severe disease	Increased TEd and TEh; decreased resting I/V slope in severe disease	[12, 61]
Acquired neuromyotonia	No change	Increased subexcitability or no change	No change	[15, 135]
Benign cramp fasciculation syndrome	No change	No change	No changes in conventional measures; decreased TEh at −70 and −100%	[136, 137]

I/V = current threshold relationship; TEh = threshold electrotonus (hyperpolarizing direction); TEd = threshold electrotonus (depolarizing direction); RRP = relative refractory period