Deformation in little finger without sensory loss, no pain

My son is 14 year old. Since last six months we noticed slightly flexion deformity in his right hand’s little finger. Skin of that finger is thickened. He has no pain, no sensory loss and no swelling. In last 20 days his left hand little finger’s skin is also getting thickened. It is hyperkerotosis?
I consulted Dermatologist, Orthopedic Surgeon, Neurologist, Rheumatologist…Every one told that it not his/ her case. Nerve Conduction Test (NCV), X-Ray, Thyroid, Blood Test all negative.