Lou gedrid disease and alzeimers do.people gets painless muscle twitches when the muscles are already dead?

Fasiculations: Lou Gehrig Disease or ALS does present with fasiculations of muscle twitching. Not usually in parkinson disease. You also see muscle atrophy however I would not call it dead muscle. ALS is a combination of lower motor and upper motor neuron disease therefore we see a combo of weakness, spasm and rigidity along with muscle wasting.

Alzheimers disease: ALS (Lou Gehrig's disease) and Alzheimer's disease are both neurodegenerative diseases. The muscles are not dead. It is the neurons that are dying. In ALS it is the motor neurons that are dying and in ALzheimer's it is the neurons of the hippocampus (temporal lobe) that are dying. People with ALS maintain their cognitive function but the Alzheimer's patients do not.