What Causes Tremor In Right Hand And Bicep Fasciculations?
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Detailed Answer:
I read your question carefully and I understand your concern.
There are several possibilities to your symptoms. One possibility for the unilateral tremor might be early stages of Parkinson's disease which typically begins on one side, more prominent at rest and improves when taking actions. This possibility would be more likely if you had other symptoms such as slowing of movement, gait and posture changes, though often they are not noticed by the patient and are found by observation by thee physician.
Another possibility for the tremor might be related to your thyroid function. Tremor may be a sign of elevated thyroid function (although typically it's on both sides). Now you suffer from diminished function, but at times when the dosage of the medication is too high tremor might appear. Now I can not say whether 150 mcg you get is high as dosage varies among patients, but it is the hormonal levels, mainly TSH which shows that. So if you haven't monitored that lately it should be measured.
Other tremor causes may include essential tremor (more commonly on both sides, increases on action, influenced by anxiety, usually have other family members), a history of alcoholism, or a brain lesion like a stroke (which is more acute and has other accompanying symptoms usually).
One other cause which may also be related to the fasciculations you describe would be cervical myelopathy, damage to spinal cord by spinal issues. The fact that you have had a prior fusion means you may be a predisposed person. Also even if the fusion procedure was executed perfectly and there are issues in the levels it involved, because of the limited mobility at those levels (C3-4-5) other levels may be exposed to an increased load, thus being more prone to have degenerative changes over the years.
So a neurological exam is the first step to orient the diagnosis, in order to check for signs of parkinsonism, stroke, muscular weakness, increased reflexes etc. If a cervical issue is suspected a neck MRI might be required and if in doubt electrical studies (nerve conduction studies/electromyography).
I remain at your disposal for other questions.