Practical neurology
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Patients who are recovering from critical illness may be weak and difficult to wean from ventilatory support as a complication of their underlying disorder, intercurrent events or treatment given during prolonged intensive care. These patients are difficult to assess because of the severity of their weakness and any accompanying encephalopathy. It is essential to undertake a meticulous review, including assessment of any septic, hypoxic or metabolic derangements and a detailed look at the dosage and duration of medication including antibiotics, neuromuscular junction blocking agents and sedation. If a primary underlying neurological cause or an intercurrent event have been excluded, the likeliest cause of weakness is one of the neuromuscular complications of critical care such as: critical care polyneuropathy, an acute axonal neuropathy which develops in patients with preceding sepsis or multi-organ failure; the use of neuromuscular junction blocking agents or steroids; and critical illness myopathy, which is the most common cause of critical care related weakness.
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Neurologists should be able to anticipate and recognise the onset of respiratory failure in patients with neuromuscular disorders. Symptoms will differ depending on the speed of onset of the respiratory muscle weakness. Careful monitoring of respiratory function is particularly important in acute disorders such as Guillain-Barré syndrome. ⋯ Patients with Guillain-Barré and other acute conditions may require short-term ventilatory support in the intensive care unit. Patients with some chronic disorders, such as motor neuron disease and Duchenne dystrophy, can be successfully treated with non-invasive ventilation, usually in collaboration with a respiratory physician. New-onset weakness of limb and respiratory muscles in the intensive care unit is usually due to critical illness myopathy or critical illness polyneuropathy, and treatment is supportive.
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Foot drop is a common and distressing problem that can lead to falls and injury. Although the most frequent cause is a (common) peroneal neuropathy at the neck of the fibula, other causes include anterior horn cell disease, lumbar plexopathies, L5 radiculopathy and partial sciatic neuropathy. And even when the nerve lesion is clearly at the fibular neck there are a variety of causes that may not be immediately obvious; habitual leg crossing may well be the most frequent cause and most patients improve when they stop this habit. ⋯ Nerve conduction and electromyographic studies are useful adjuncts in localising the site of injury, establishing the degree of damage and predicting the degree of recovery. Imaging is important in establishing the cause of foot drop be it at the level of the spine, along the course of the sciatic nerve or in the popliteal fossa; ultrasonography, CT and MR imaging are all useful. For patients with a severe foot drop of any cause, an ankle foot orthosis is a helpful device that enables them to walk better and more safely.