How does the temporal pattern of weakness or pain aid in diagnosis?
1. Abrupt onset of weakness is more characteristic of Guillain–Barré syndrome, poliomyelitis, and hypokalemic periodic paralysis.
2. Intermittent weakness may occur with myasthenia gravis, the rare causes of metabolic myopathy, and hypokalemic periodic paralysis.
3. Gradual onset of weakness or pain is typical of most muscle diseases, including inflammatory myopathies, muscular dystrophies, and endocrine myopathies, as well as most neuropathies. It may also occur with myasthenia gravis.