Unilateral weakness often indicates which of the following conditions?

Unilateral weakness is a hallmark sign of a stroke, which occurs when there is an interruption of blood flow to the brain, leading to damage in the areas responsible for motor control. The brain controls movement on the opposite side of the body, so a stroke affecting one hemisphere can result in weakness on the opposite side. This is why patients experiencing unilateral weakness should be evaluated promptly for the possibility of a stroke.

Other conditions listed, while they can cause weakness, do not typically present with isolated unilateral weakness in the same acute way that a stroke would. For example, muscle strain usually causes localized pain and weakness in a specific muscle group but does not typically present with unilateral weakness affecting the entire side of the body. Peripheral neuropathy often results in symptoms of numbness, tingling, or weakness, usually in a "stocking-glove" distribution, and is not confined to one side. Autoimmune disorders may result in generalized weakness or fatigue but are less likely to cause acute unilateral weakness as seen with strokes. This understanding underscores the distinct clinical implications of unilateral weakness in the context of a potential stroke.