Primary Hypertrophic Osteoathropathy - Classification

Classification

PDP is one of the two types of hypertrophic osteoarthropathy. It represents approximately 5% of the total hypertrophic osteoarthropathy cases. The other form is secondary hypertrophic osteoarthropathy (SHO). SHO usually has an underlying disease (e.g. cardiopulmonary diseases, malignancies or paraneoplastic syndrome). Unlike SHO, PDP does not have an underlying disease or malignancy.

PDP can be divided into three categories:

• The complete form occurs in 40% of the cases and can involve all the symptoms but mainly pachydermia, periostosis and finger clubbing. This is also referred to as the full-blown phenotype.
• The incomplete form occurs in 54% of the cases and is characterized by having mainly effect on the bones and thereby the skeletal changes. Its effect on the skin (causing for instance pachydermia) is very limited.
• The fruste form occurs in only 6% of the cases and is the opposite of the incomplete form. Minor skeletal changes are found and mostly cutaneous symptoms are observed with limited periostosis.

The cause of these differentiating pathologies is still unknown.