Fasciculations can be healthy, or signify which type of motor neuron disease?

• A. Upper
• B. Lower
• C. Spinal
• D. Peripheral

Answer: (B)

Fasciculations reflect instability or loss of function in the lower motor neurons. They are spontaneous discharges of motor units that become visible as brief muscle twitches. In healthy individuals, occasional fasciculations can occur and are not a sign of disease. But when the lower motor neurons are affected by disease, such as the degeneration of anterior horn cells or their axons, the remaining motor units fire irregularly, producing visible twitches. Upper motor neuron problems, in contrast, produce signs like spasticity, increased reflexes, and certain reflex changes, rather than prominent fasciculations as a defining feature. Peripheral neuropathies can cause twitching too, but the question centers on motor neuron disease, where fasciculations most strongly indicate lower motor neuron involvement.