[13] A special form of clubbing is hypertrophic pulmonary osteoarthropathy (HPOA), known in continental Europe as Pierre Marie-Bamberger syndrome.

[citation needed] Primary hypertrophic osteoarthropathy is HPOA without signs of pulmonary disease.

This form has a hereditary component, although subtle cardiac abnormalities can occasionally be found.

This condition has been linked to mutations in the gene on the fourth chromosome (4q33-q34) coding for the enzyme 15-hydroxyprostaglandin dehydrogenase (HPGD); this leads to decreased breakdown of prostaglandin E2 and elevated levels of this substance.

Associated conditions may be identified by taking a detailed medical history—particular attention is paid to lung, heart, and gastrointestinal conditions—and conducting a thorough clinical examination, which may disclose associated features relevant to the underlying diagnosis.

When the distal phalanges (bones nearest the fingertips) of corresponding fingers of opposite hands are directly opposed (place fingernails of same finger on opposite hands against each other, nail to nail), a small diamond-shaped "window" is normally apparent between the nailbeds.