In evaluating worsening lower extremity weakness, what types of questions are important to ask first?

The causes of lower extremity weakness can be broad, and it is important to be aware of conditions that necessitate emergency management. Traumatic spinal cord injury can result in myelopathy, pararparesis, and bowel and bladder symptoms. The patient should be asked of any recent falls or accidents, history of low back pain and vertebral disc herniation, as well as new bowel or bladder symptoms. If the injury is due to a vertebral fracture or dislocation, immediate neurosurgical management may be needed for decompression and possible fusion of the involved vertebrae.

Onset and timing of the weakness can assist in narrowing down the possible causes. Sudden and severe weakness suggests an associated trauma resulting in acute spinal cord compression. It could also suggest a vascular etiology such as an acute infarction, arteriovenous (AV) malformation, or acute hemorrhage involving the spinal cord. A gradual onset and subacute course of weakness can suggest an inflammatory cause (multiple sclerosis, transverse myelitis, or Guillain-Barré syndrome), spinal abscess, neoplasm, or compressive disc herniation. A slow and insidious progression of weakness can indicate a metabolic process associated with peripheral neuropathy such as diabetes, vitamin B12 deficiency, or a paraneoplastic process.

Determining if and when sensation is affected can provide further insight into the etiology of the weakness. A pure myopathic process should not present with associated sensory symptoms. Conditions that affect the neuromuscular junction, such as botulism and myasthenia gravis, would also lack sensory impairment. Numbness or decreased sensation preceding weakness suggests a neuropathic process such as diabetic neuropathy because sensory nerve fibers tend to be smaller and more prone to metabolic damage before larger nerve fibers that innervate muscles. Decreased or absent sensation occurring simultaneously with severe weakness may indicate a concurrent process affecting a similar system such as an upper motor neuron process involving the brain or spinal cord.

What questions on the review of systems are also important to note in this case?

Considering the severe and progressive nature of the patient’s weakness, respiratory status must be noted. Symptoms that would be concerning for respiratory compromise include impaired swallowing and difficulty coughing. Fever and other signs of infection can point toward the presence of a spinal abscess. Unexplained weight loss and increased fatigue can point toward a neoplastic process such as a tumor or metastatic lesions. The presence of a rash, muscular pain, or viral symptoms could suggest an autoimmune cause for weakness, such as dermatomyositis, polymyositis, or polymyalgia rheumatica.

How is muscle strength assessed and graded on physical exam?

Muscle strength is graded from 0 to 5 and uses examiner-provided resistance and then gravity as references. A 5 is given for full and normal muscle strength, which the examiner is unable to break. A grade of 4 represents muscle strength where the patient is able to partially resist the examiner. Grade 3 is when the patient is unable to resist the examiner but able to move the limb against gravity through a full range of motion. A grade of 2 represents full range of motion with gravity eliminated. An example of grade 2 is movement along the plane of a bed, but not up and off of it. A grade of 1 is given to trace muscle movement or contractions, and a grade of 0 is when no muscle contractions are detectable. A + or − may also be added to the numerical grade and represents strength slightly greater or less than the associated numerical grade.

What signs are concerning for respiratory compromise in acute neuromuscular disease?

When evaluating worsening or rapidly progressive neuromuscular disease, it is important to determine whether the muscles of respiration are involved. They can be grouped into the upper airway muscles, muscles of inspiration, and muscles of expiration. A bulbar palsy can lead to impaired swallowing, and weakness involving the muscles of expiration can result in difficulty clearing secretions. Both of these conditions put a patient at risk for an aspiration pneumonia. Issues with inspiratory muscles can result in impaired lung expansion, ventilation/perfusion mismatch, and difficulty with adequate oxygenation. Symptoms to be aware of include severe and rapidly worsening generalized weakness, dysphagia, dysphonia, new dyspnea with exertion or rest, and trouble swallowing. Signs signaling the need for admission to a monitored setting include rapid and shallow breathing, tachycardia, accessory muscle use, and orthopnea. Although patients can be monitored with telemetry, the rapid nature of neuromuscular disease easily warrants care in an intensive care unit (ICU) should there be any concern regarding the patient’s breathing.