Periostosis

Pachydermoperiostosis (PDP) is a rare genetic disorder that affects both bones and skin. Other names are idiopathic hypertrophic osteoarthropathy or Touraine-Solente-Golé syndrome. It is mainly characterized by pachydermia (thickening of the skin), periostosis (excessive bone formation) and finger clubbing (swelling of tissue with loss of normal angle between nail and nail bed). Pachydermoperiostosis (PDP) is a rare genetic disorder that affects both bones and skin. Other names are idiopathic hypertrophic osteoarthropathy or Touraine-Solente-Golé syndrome. It is mainly characterized by pachydermia (thickening of the skin), periostosis (excessive bone formation) and finger clubbing (swelling of tissue with loss of normal angle between nail and nail bed). This disease affects relatively more men than women. After onset, the disease stabilizes after about 5–20 years. Life of PDP patients can be severely impaired. Currently, symptomatic treatments are NSAIDs and steroids or surgical procedures. In 1868, PDP was first described by Friedreich as ‘excessive growth of bone of the entire skeleton’. Touraine, Solente and Golé described PDP as the primary form of bone disease hypertrophic osteoarthropathy in 1935 and distinguished its three known forms. PDP has a number of visible symptoms. Most important clinical features are: pachydermia (thickening and wrinkling of the skin), furrowing of the face and scalp, periostosis (swelling of periarticular tissue and shaggy periosteal new bone formation of long bones) and digital clubbing (enlargement of fingertips). Other features include excessive sweating, arthralgia and gastrointestinal abnormalities. An overview of all symptoms is provided in table 2. Table 2. Overview of symptoms Two genes have been associated with this condition: hydroxyprostaglandin dehydrogenase 15-(NAD) (HPGD) in chromosome 4 (4q34.1) and solute carrier organic anion transporter family member 2A1 (SLCO2A1) in chromosome 3 (3q22.1-q22.2). This syndrome occurs if both copies of either gene are mutated (autosomal recessive inheritance) Although the pathogenesis of PDP is still not fully understood, two theories have been suggested: Recently, it has been suggested that the locally acting mediator ] (PGE2) plays a role in the pathogenesis of PDP. In PDP patients, high levels of PGE2 and decreased levels of PGE-M (the metabolite of PGE2) were observed. PGE2 can mimic the activity of osteoblasts and osteoclasts (respectively building and breaking down bone tissue). This is why acroosteolysis and periosteal bone formation can be explained by the action of PGE2. Furthermore, PGE2 has vasodilatory effects, which is consistent with prolonged local vasodilation in digital clubbing.