I have the same issue with my right hand. EMG always come back as carpal tunnel. Two surgeries later plus release of the ulnar nerve have done nothing. Muscle below right thumb is wasting away. Other hand is fine.
Neurologist tentatively diagnosed it as Inclusion Body Myositis[IBM] which is a rare, progressive muscle disorder causing gradual weakness often starting after the age of 50.
I need several more MRIs and a muscle biopsy to confirm which have not been performed yet. There is no cure so I just have to live with it.