EMG + nerve conduction studies quick and dirty as I tried to learn in my neuro rotation:

EMG

• insert needle: get some activity bc the needle can irritate the muscle fibers, you can tell bc when you insert the needle, you hear noise until you stop moving the needle
• healthy muscle/nerves: at rest, you will see minimal electrical activity except for the occasional muscle endplate potential. All other electrical activity at rest is pathologic and means you got yourself a problem
• Fibrillations: come from denervated muscle fibers, which just spontaneously fires like crazy cause they lost their contact with their nerve and they lonely AF. These happen several days-weeks after inciting denervation, not immediately. this is what we would see with ALS
• Myotonic discharges: still don't completely understand this one, but I think the gist is they can occur as you move the needle around in healthy muscle, but pathologically more indicative of a myotonic muscular disorder or other myopathy not nerve related (I could still be completely wrong about this one)
• recently denervated muscle: low to no activity. Nerves regrow slowly over a period of a few weeks and will show more electrical activity on EMG, described as low amplitude and short duration (another answer choice)

Nerve conduction

• ALS is a motor neuron disease- meaning it won't affect sensory- so you don't expect to see changes in sensory responses.

Ill be the Cowboy.

Diagnosis: ALS

Multispike and fasciculation potentials Complex, repetitive discharges occur in ALS of long duration, as they do in other chronic neurogenic atrophic conditions. These are regularly discharging multispike potentials that are time-locked. Other than an EMG finding associated with a chronic neurogenic atrophic condition, this finding has no other unique significance.

Fasciculation potentials are seen frequently but not invariably in ALS. Their presence is not specific to ALS; they may occur in other conditions, some completely benign.

• Young man with chronic weakness who has UMN lesions (Babinski sign) and LMN lesions (atrophy, fibrillations), most consistent with amyotrophic lateral sclerosis (ALS), which leads to fibrillation potential in multiple muscles on electromyography
• Key idea: ALS often presents with weakness in hands, difficulty swallowing (like in this patient), and changes to voice

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Tumbleweed