In amyotrophic lateral sclerosis (ALS), what is the most common onset pattern?

• A. Limb onset
• B. Bulbar onset
• C. Respiratory onset
• D. Trigeminal onset

Answer: (A)

Weakness in ALS most commonly begins in the limbs. In the majority of patients, the first symptoms are focal limb weakness and muscle wasting, often presenting asymmetrically in one arm or leg and sometimes with fasciculations. This limb-onset pattern reflects early degeneration of motor neurons in the spinal cord and brainstem that control limb muscles. As the disease progresses, signs of both upper and lower motor neuron involvement spread to other regions.

Bulbar onset, where speech and swallowing are affected first, occurs but is less common. Respiratory onset at presentation is relatively rare and tends to appear later as respiratory muscles become involved. Trigeminal onset is not a typical initial pattern.

So the most common onset pattern is limb onset.