Critical illness neuropathies

A number of patients admitted to intensive care units for non-neurological disorders develop neuromuscular complications. These patients present with an acute flaccid generalized weakness that may or may not be accompanied by sensory symptoms. There are two main conditions, namely critical illness polyneuropathy and neuromuscular disorder related to the use of neuromuscular blocking agents. These conditions differ in several ways. Critical illness polyneuropathy occurs usually after long stays (weeks) in intensive care units. It concerns patients presenting with a multiple organ dysfunction syndrome, and often sepsis. The polyneuropathy is axonal and implies both sensory and motor fibres. Its pathophysiology remains unclear. Mortality is as high as 60 p.cent and relates to the medical, rather than to the neurological condition. In survivors recovery may be complete, although over a period of months. Neuromuscular disorder related to the use of neuromuscular blocking agents occurs on average after 10 days. It most often concerns patients admitted to intensive care units for acute respiratory failure, mainly asthma or adult respiratory distress syndrome, that may require mechanical ventilation, use of neuromuscular blocking agents and steroids. A purely motor deficit is usually first noticed when curarisation is discontinued. Electromyography discloses fibrillation potentials in all muscles, as well as myopathic changes. Muscle biopsy demonstrates necrosis and a deficit in myosin filaments. In severe cases, injury to distal motor axons probably occurs. Recovery is usually excellent over a few weeks. Recently, replacement of neuromuscular blocking agents by sedatives has notably reduced the occurrence of this disorder. Critical illness neuropathies often cause difficulty in weaning patients from the respirator. They prolong the stay in the intensive care unit, thereby increasing the risks of complications for the patients. Course of these neuromuscular disorders is usually favorable, however sometimes with sequelae.