CRITICAL ILLNESS NEUROMYOPATHY

Abbreviations CIP critical illness polyneuropathy CIM critical illness myopathy CMAP compound muscl action potentials SNAP sensory nerve action potential EMG electromyogram SIRS systematic inflammatory response syndrome

HISTORICAL REVIEW In 1955 observed a polyneuropathy after shock or cardiac arrest In 1961 described “coma-polyneuropathies” In 1971 described a polyneuropathy in patients with burns in 1977 severe polyneuropathy about septic patients

By 1983 the term “critical illness polyneuropathy”（CIP） was applied Recently the termed “critical illness myopathy ”（CIM） was applied

Studies about Aetiologyvariously The various factors associated with the SIRS CIP and CIM (Fig. 1) A simplified depiction of theoretical mechanisms of dysfunction in CIP and CIM.(Fig. 2 ) Disorder of microcirculation（Fig. 3)

Figure. 1 Adapted with permission from Bolton.

Adapted with permission fromBolton25. Figure. 2

Figure.3 Schematic, theoretical presentation of disturbances in the microcirculation to various organs, including brain, peripheral nerve, and muscle, in SIRS.

Incidence 50%–70% SIRS 20%–50% ICU

Clinical Features • Tendon reflexes absent or decrease • Weakness of limb and respiratory muscle • Tendon reflexes absent or decrease •Distal loss to pain, temperature, and vibration

Diagnosis The diagnostic criteria for CIP are shown in following Table

Diagnostic criteria for CIP The patient is critically ill (sepsis and multiple organ failure,SIRS) Difficulty weaning patient from ventilator afternonneuromuscular causes such as heart and lung diseasehave been excluded Possible limb weakness Electrophysiologic evidence of axonal motor and sensory polyneuropathy

Electrophysiologic Features Decline in the CMAP amplitude firstly (Fig. 4) Dcline in the SNAP amplitude Motor unit potentials may be reduced in number Single-fiber EMG indicate dysfunction of terminal motor axons

Measurement of compound thenar muscle action potentials at the onset of sepsis (A) and 3 weeks later (B). FIG.4

Morphologic Features Peripheral axonal degeneration. Moderate loss of dorsal root ganglion cells Central chromatolysis of anterior horn cells No inflammation in the peripheral nervous system

Muscle biopsy Acute and chronic denervation Occasional myopathic changes

Pathology of critical illness polyneuropathy Pathology of critical illness polyneuropathy. There is chromatolysis of anterior horn cells (A); severe axonal degeneration in this cross-section of superficial peripheral nerve (B) and longitudinal section of deep peroneal nerve (C); and acute and chronic denervation of intercostal muscle (D)

Differential Diagnosis Axonal variants of Guillain–Barre′ syndrome Develop earlier Often associated with CJ infection Abnormal cerebral spinal fluid

Transient neuromuscular blockade Repetitive nerve stimulation Measurement of anti-MuSK (muscle specific receptor tyrosine kinase) antibodies

Treatment Treatment of sepsis and multiple organ dysfunction syndrome Management of difficulty in weaning from the ventilator Attempts at direct treatment of CIP (still unproven) Physiotherapy and rehabilitation

Two newer research approaches are being explored Intensive insulin therapy The administration of recombinant human activated protein C

Prognosis Recovery depends on the distance Recovery for weeks in mild cases and months in severe cases Slowing of nerve conduction may have a poor prognosis

Incidence At least one-third of ICU patients（ treated for status asthmaticus） In 7% of patients after transplantation

Clinical Features Major feature is flaccid weakness Tendon reflexes depressed Ophthalmoplegia may be present Myalgias are uncommon

Diagnosis Diagnostic criteria of CIM ● SNAP amplitudes 80% of the lower limit of normal ● Needle EMG with short-duration, low-amplitude MUPs with early or normal full recruitment, with or without fibrillation potentials ● Absence of a decremental response on repetitive nerve stimulation

● Muscle histopathologic findings of myopathy with myosin loss ● CMAP amplitudes 80% of the lower limit of normal in two or more nerves without conduction block ● Elevated serum creatine kinase (CK） ● Demonstration of muscle inexcitability *For a definite diagnosis of critical illness myopathy, patients should have all of the first five features.

Electrophysiologic Features Nerve conduction studies Low-amplitude CMAPs Long duration CMAPs Normal SNAPs Phrenic nerve conduction normal latencies diaphragm CMAP amplitudes reduce

EMG Fibrillation potentials and positive sharp Motor unit potentials low amplitude and short duration Electrical inexcitability by direct needle stimulation

Morphologic Features Features of the histopathology in thick filament myosin loss (Fig. 5) Electron microscopy reveals selective loss of thick (myosin) filaments (Fig. 6) Inflammatory changes are conspicuously absent

Figure. 5 Muscle histopathology in a critically ill patient with thick filament myosin loss. (original magnification, 100) (courtesy of Dr. Andrew Engel).

Figure. 6 Electron microscopy of muscle in CIM Figure. 6 Electron microscopy of muscle in CIM. (original magnification, 44,000) (courtesy of Dr. Andrew Engel).

6. Differential Diagnosis CIP Direct needle stimulation of the muscle Electrical inexcitability in CIM There is a response in CIP (Fig. 7) Serum CK Muscle biopsy

FIGURE. 7 Results of direct and indirect muscle stimulation FIGURE. 7 Results of direct and indirect muscle stimulation. CMAPs from the anterior tibial muscles of a patient with critical illness polyneuropathy (left) and critical illness myopathy (right).

Subtypes of CIM Muscle morphologic Differentiating feature of neuromuscular disorders in critical illness Table 1.

Treatment No specific therapy available as to now Positioning to avoid additional nerve damage by pressure Avoid administering muscle relaxants and corticosteroids

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