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Discussion Starter · #1 ·
A 60-year-old man develops a tremor in his fingers. The tremor is most pronounced when he reaches for his coffee cup or points to an object. Which of the following components of the motor system is most likely to be involved?

(A) Basal ganglia
(B) Cerebellar hemisphere
(C) Cerebellar vermis
(D) Frontal eye field
(E) Motor nucleus of the thalamus
 

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This is a characteristic case of INTENTION tremor, i.e. tremor that is pronounced when the pt is moving and especially aggravates when he/she tries to reach an "intended for" object (thus the name). The lesion lies somewhere in the cerebellar hemispheres (correct answer is B).

The major differential (in clinical practice & undoubtedly for the USMLE) is resting tremor, i.e. tremor that is more pronounced when the limb is at rest. Resting tremor is characteristic in the context of Parkinson's disease, where the lesion lies indeed in the thalamostriate component of the basal ganglia (answer E is NOT correct, sorry :)).

Let me express some personal experience here, where intention tremor has also been observed in some cases of idiopathic tremor. However, this is not the case here and it definitely should not be the case in the actual USMLE exam (although one can never know...).
 

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Discussion Starter · #4 ·
thank u ath.pantelis

i answered basal ganglia because i immediately assumed parkinson. sigh.. ok ok. so now ill have to look out intention or rest as clue words. so yeah parkinson would be basal ganglia but if intention tremor then cerebellar hemisphere. is cerebellar hemisphere incoordination somewhat related to alcoholic gait? as in, is it due to the effect on the cerebellar hemisphere that alcoholics may have gait? i know alcohol affects the cerebellar too. ryte?:confused:
 

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The classic gait disturbance associated with chronic alcohol abuse is ataxia, indeed. However, this is basically due to thiamine deficiency and constitutes the "Wernicke" component of the Wernicke-Korsakoff syndrome ("Korsakoff" is accompanied by amnesia, confabulation & hallucinations). The Wernicke component is also characterized by nystagmus & opthalmoplegia. So, any gait disturbance in the context of chronic alcohol abuse is a "korsakoid' variant, if I am allowed the term. (Also, don't forget flapping tremor, a sign of hepatic encephalopathy, that is associated with cirrhosis, which in turn is associated with chronic alcohol abuse. But in this case, the reason is impaired ammonia metabolism, it is not a sequella of alcohol).

Gait disturbance in acute alcohol intoxication may also present in a similar manner, ranging within a spectrum (from impaired co-ordination to ataxia, to severe co-ordination disturbance, to coma and death) according to the amount of alcohol consumed.

In either case, one cannot definitely determine that the lesion lies within this or the other area of the CNS, because the cause is rather generalized (impairment of glucose metabolism in the case of chronic alcohol abuse; generalized & direct toxic effect of alcohol on the neurons, in the case of acute alcohol intoxication). It is possible that the cerebellum and the cerebellar projections to the motor system are more susceptible to damage than other areas of the CNS, perhaps due to variations of the blood brain barrier, but I am not familiar with any consistent data:confused:.

Finally, I'd like to add that it is remarkable that alcohol has beneficial effects on patients with idiopathic tremor (NEUROLOGY 2005;65:96-101). This may suggest that alcohol shows some predisposition for the system of co-ordination, but I am not sure that this could be proven by, let's say, a pathologic exam of the cerebellum or its projections.

Any further input would be welcome!
 
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