I am not sure, clubbing of the fingertips, (the pads become enlarged) can be caused by cyanotic heart disease, advanced pulmonary disease, biliary cirrhosis, Colitis, chronic dysentery and thyrotoxicosis, I highly doubt your son has any of these conditions. There is a type of eczema that can cause bumps on the fingertip pads the lesions look like blisters. E/W I am at a loss