micrographia is quite different from writers cramp. Writers cramp is not a problem ofParkinson's disease. If your uncle has Parkinson's disease it is most likely not due to writers cramp. So I have written this as considering your uncle doesn't have writers cramp and that that is a false diagnosis. The shaking (tremor) usually disappears on the concentrating on moving so is usually not such a big problem as you hand writing causes the movement. The problem in micrographia is considered due to hypokinesia which is loss of the size of the movement - the size of the movement is affected due to failing of the scaling of the movement by the part of the brain that is affected. this is what produces the tiny hand writing and small steps in walking.
Two strategies you could try is having some large hand writing on the line above and getting your uncle to practice copying the large handwriting. this often has a temporary effect of increasing the handwriting for some time. But the exercise needs to be repeated, for example each day doing a bit of practice
An alternative strategy is to practice hand writing while not looking at the hand (eg keep the eyes closed):
http://www.bcm.edu/neurology/pdf/pos...n%20PD_MDS.pdf
there is usually a general loss of fine manipulation skills in the hand over and above micrographia. Keeping the hand strong and practising manipulation tasks each day may help slow down the decline in hand function. However there is a fine line between "fighting the disease" - that is where you exercise to overcome the impairments and where there needs to be some acceptance of the loss of function and thinking about alternative strategies. On the whole you are better off doing what he can to keep the function. And keeping fit generally is really important - exercising every day.
Is your uncle on levadopa or other Parkinson's medications?