Hypertrophic osteoarthropathy (HOA) was first described in 1868 as "hyperostosis of the entire skeleton". It has also been mistaken for acromegaly. In 1887-1888 the first description was given of a dermatological disorder "cutis verticis girata" which coexisted with the peculiar bone anomalies of HOA. In 1890 HOA was named "osteoarthropatie hypertrophiante pneumique". Later a distinction was made between the rare idiopathic (or primary) form, also called "pachydermoperiostosis" and the more common secondary form due to concomitant disorders involving the lungs and pleura. The primary form usually develops shortly after puberty or during adolescence and has not been found associated with underlying disease. Secondary HOA was initially called "hypertrophic pulmonary osteoarthropathy" because it is frequently associated with various malignancies or chronic infections of the lung and pleura. Later, since the site of primary disease may be elsewhere, involving the gut and the cardiovascular, hepatobiliary and endocrine systems, this designation fell into disuse. In some cases of secondary HOA, the osteoarthropatic and facial skin changes subside after pneumonectomy or other procedures. A disease resembling human HOA has been also described in dogs.