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A 28-year-old woman presents to the urgent care clinic complaining of weakness. For the past week, she has had weakness and numbness in her right arm and bouts of dizziness. The symptoms became worse 2 days ago but have since stabilized.

  • What additional questions would you ask to learn more about her weakness?
  • Can you localize her lesion to a specific anatomic site?
  • How can you use the patient history to determine if the patient requires urgent intervention for weakness?
  • How do the duration and evolution of symptoms help narrow the differential diagnosis?

In approaching a patient with a complaint of weakness, the physician must first determine whether the patient has functional or motor weakness. Many patients who complain of weakness are actually suffering from functional weakness due to asthenia, the sensation of exhaustion or lethargy despite normal muscle strength, or increased fatigability, the tiring of muscles with multiple repetitions. Functional weakness may be caused by a variety of conditions including cancer, infection, metabolic derangements, inflammatory diseases, and psychiatric disorders. In these conditions, the patient has trouble completing activities of daily living because of a lack of physical or emotional energy, but has normal muscle strength. Another potential masquerader of weakness is pain that prevents a patient from completing specific activities despite retained muscle strength. Patients with neuromuscular weakness are unable to move their muscles at full strength despite maximum effort and optimization of modifiable factors.

The first step in evaluating any patient complaining of weakness is to distinguish functional weakness from neuromuscular weakness. The history should be completed systematically with a focus on the onset, the evolution of symptoms, and location of the lesion along the motor pathway. Although all patients with weakness warrant a careful evaluation, this chapter focuses on patients whose history suggests true weakness of the muscles. For the remainder of this chapter, the term "weakness" will mean neuromuscular weakness.

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Ascending paralysisMotor weakness that begins in the feet and progressively moves up the body.
Bulbar symptomsWeakness in the muscles of the face and tongue, resulting in difficulty speaking, swallowing, and smiling.
Descending paralysisMotor weakness that begins in the face and progressively moves down the body.
Distal weaknessWeakness in the distal extremities (eg, foot drop).
HemiparesisWeakness on one side of the body.
MonoparesisWeakness of one limb.
ParaparesisWeakness of both legs.
Proximal weaknessWeakness in proximal muscles (eg, shoulder girdle, quadriceps) resulting in difficulty standing up from a seated position or raising arms above head.
TetraparesisWeakness of all 4 limbs.
Todd's paralysisReversible weakness following a seizure.
Upper motor neuron lesionsAbnormalities of motor pathways that descend from the central nervous system to the alpha motor neurons, resulting in spasticity, hyperreflexia, and increased muscle tone.
Lower motor neuron lesionsAbnormalities of the alpha motor neuron in the brainstem or spinal gray matter, resulting in muscle atrophy, hyporeflexia, and ...

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