Table 1.

Diagnostic criteria for ICU-acquired weakness, critical illness polyneuropathy, and critical illness myopathy

	ICUAW
Clinical diagnosis [69]	Minimum criteria for diagnosing ICUAW: 1, 2, 3 and 5 or 4 and 5 (1) Generalized weakness developing after the onset of critical illness (2) Weakness is diffuse (involving both proximal and distal muscles), symmetric, flaccid, and generally spares cranial nerves (3) MRC sum score less than 48, or mean MRC sum score less than 4 in all testable muscle groups noted on at least two occasions separated by 24 h (4) Dependence on mechanical ventilation (5) Causes of weakness not related to the underlying critical illness have been excluded
	CIP	CIM
Electrophysiological diagnosis [58]	Definite CIP: all of the following criteria Probable CIP: criteria 1, 3, 4 and 5 (1) The patient is critically ill (2) Diagnosis of ICUAW established (3) CMAP amplitudes less than 80% of the lower limit of normal in at least two motor nerves (4) SNAP amplitudes less than 80% of the lower limit of normal in at least two sensory nerves (5) Absence of a decremental response on repetitive nerve stimulation	Definite CIM: all of the following criteria Probable CIM: criteria 1 and 3–6 (1) The patient is critically ill (2) Diagnosis of ICUAW established (3) CMAP amplitudes less than 80% of the lower limit of normal in at least two nerves (4) SNAP amplitudes normal (5) EMG with short duration, low-amplitude MU potentials with early or normal full recruitment, with or without fibrillation potentials in collaborative patients; or reduced muscle action potential amplitude less than 3 mV and muscle/nerve action potential amplitude around 1 on DMS in noncollaborative patient (6) Absence of a decremental response on repetitive nerve stimulation (7) Muscle histology consistent with myopathy
Muscle biopsy [58,70]	Features of denervation and reinnervation with small muscle fibers, fiber-type grouping, and fiber group atrophy	Thick filament myopathy with a selective loss of myosin filaments; muscle necrosis; acute diffuse necrotizing myopathy.
Nerve biopsy [58,70,71]	Widespread axonal degeneration of both motor and sensory nerves.	Normal

CIM, critical illness myopathy; CIP, critical illness polyneuropathy; CMAP, compound muscle action potential; DMS, direct muscle stimulation; EMG, electromyogram; ICUAW, ICU-acquired weakness; MRC sum score, Medical Research Council sum score; MUP, motor unit potential; SNAP, sensory nerve action potential.