The rate of symptom onset helps suggest likely pathophysiology: Nearly instantaneous (usually seconds, occasionally minutes): Ischemic or traumatic Hours to days: Infectious or toxic-metabolic Days to weeks: Infectious, toxic-metabolic, or immune-mediated Weeks to months: Neoplastic, or degenerative, or occasionally infectious due to chronic central nervous system (CNS) infection (eg, fungal infection) Degree of symmetry also provides clues.