Arm Tingling Nunbness Incoordination

  I have been treated for Central Hypothyroidism for the past 20 months. Over the past 3 years I have
  had tingling, numbness, incordination and perceived weakness in my left arm. Last week my endocrinologist
   said these symptoms should be resolving now that I am fully responding to the thyroid repalcement. He tested (pending) for
  Vitamin B12 deficiency since my symptoms worsen when I go off my daily vitamins (Super B Complex + OneSource multivitatmin. )
  He said  I had indications of of an Intention Tremor and refereed me to see a Nuerologist (scheduled for 3/3/99). My tremor occurs when
  I grasp something with my left hand. I need to squeeze quite tightly to invoke the tremor. I have read that Intention Tremor
  is present when for something and is visble when touching the finger to the nose - I don't seem to have trouble with these tasks.
  Is this a true Intention tremor or is it an isometric tremor ? My left arm seems to have internal twitching going
  on all the time - particularly using the computer keyboard.
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We distinguish tremors based on their characteristics.
A resting tremor occurs when there is NO activation of agonist or antagonist muscles. For example, you are sitting with your arms in your lap or in the arm chair armrests, watching TV, not paying any attention to the arms, and the tremor comes.
A postural tremor occurs when one is maintaining a posture such as outstretched arms, and there is an overlap with kinetic or action tremor, in which the tremor increases with use of the arm. For example, people with postural tremors often notice difficulty bringing a cup of water to their mouth.
Intention tremor is less helpful as a term. It is supposed to mean the tremor gets worse with intentional movement, but I find "action" or "kinetic" tremor more helpful conceptually.
None of these tremor types is itself a diagnosis. However, there are some clues to help your neurologist provide a diagnosis. For example, resting tremor in combination with a certain incoordination and slowness of movement of limbs and perhaps balance difficulties makes a neurologist think of Parkinson disease (PD). Pure postural tremor, with no other neurologic signs, makes one think of benign essential tremor (ET).
A neurologist experienced in the diagnosis and treatment of movement disorders will be able to comment whether your cerebellum appears to be working OK, and should be able to suspect and systematically evaluate the possibility of dystonia, which can produce a tremor such as you describe.
Dystonia is itself not a disease, though many people have it an nothing else and we often don't find a specific cause. Dystonia is a disorder of maintenance of posture (if it appplies to you, then the postural dyscontrol would affect your arm). Often, it shows up as abnormal patterns of muscle contractions, causing unusual (limb) postures, jerking mvoements, and sometimes tremor.
It is, of course, impossible to diagnose tremor in this forum. However, you will be able to take this information and understand the approach of your neurologist when you are evaluated, and perhaps have a basis for understanding his/her analysis and explanation.
I hope this helps. CCF MD mdf.