Finger clubbing usually affects the top of the fingers on both hands. And can also affect toes. It seems to happen in stages:
- there is softening of the base of the nail (nail bed) and redness (erythema) of the skin around the nail
- the angle between the nail bed and the nail fold (the skin just below the cuticle) increases, which causes the nail to curve more than usual
- the nail and the skin around the nail look shiny, and the nail has ridges along the length of it
- the ends of the fingers look larger, giving the ‘clubbed’ appearance
Finger clubbing generally takes years to develop. But it can happen quicker in certain conditions such as a lung abscess.
Hypertrophic pulmonary osteoarthropathy (HPOA)
In the later stages of finger clubbing, extra areas of bone might form on the finger joints, wrists and ankles. This is sometimes mistaken for arthritis and is called hypertrophic pulmonary osteoarthropathy (HPOA).
Who can get finger clubbing?
Finger clubbing can be a sign of a number of underlying health conditions, particularly of the lungs or heart. This includes cancers such as lung cancer and mesothelioma. But finger clubbing can also be found in some people with thyroid problems or other conditions such as ulcerative colitis and Crohn’s disease. Many people with these conditions don’t have finger clubbing.
What causes finger clubbing?
It is not clear what causes finger clubbing. It may be due to large cells called megakaryocytes getting stuck in the small blood vessels in the tips of the fingers. Megakaryocytes are usually in the bone marrow 
and make platelets, which we need for blood clotting.
When stuck in the fingertips, the megakaryocytes start to release growth factors which lead to an increase in blood vessels and tissue growth, and a build up of fluid.
