HYPERTROPHIC PULMONARY OSTEOARTHROPATHY

Discussion

HPOA is a rare condition of uncertain etiology that is caused by an underlying lung disease. Of all the potential intra thoracic malignancies bronchogenic carcinoma and pleural tumors are the most common underlying lesions for the cause of HPOA (5-10%). Lung metastases rarely cause HPOA. Other thoracic causes of secondary HPOA are abscess, bronchiectasis and emphysema,

The association of HPOA with pulmonary metastases of an osteosarcoma is a rare occurrence with only two reported cases in literature [2],[3]. Staalman and Umans reported nasopharyngeal carcinoma metastases as the underlying cause for the development HPOA in children [4].

The classic picture of HPOA is digital clubbing, polyarthralgia and periostosis. Articular symptoms and signs are the presenting manifestations of HPOA. Pain and tenderness appear first with subcutaneous skin thickening. The wrists, elbows, knees, ankles and metacarpophalangeal joints are most commonly involved.

The stimulating factor in HPOA etiology is platelet derived growth factor (PGDF). PGDF induces tissue damage and excessive fibroblast production. In malignancy cytokines, transforming growth factor and interleukin - 1 are liberated which in turn enhance production of PGDF. Periostitis is the hallmark of HPOA and occurs usually in the metadiaphyseal regions of the ulnae, radii, fibulae and tibiae [1]. Less commonly, the femora, humerii, metacarpals and metatarsals may be involved. The typical feature is that periostitis does not extend to the epiphysis. Usually smooth multi layered laminated new bone formation is seen. Rarely simple elevation of the periosteum or periosteal cloaking may be seen.

On radionuclide bone scans, a diffuse symmetric uptake occurs in the diaphyses and metaphyses of tubular bones creating the typical "double stripe sign".

Periostitis occurs in a wide spectrum of diseases. Of this primary HPOA pachy dermoperiostitis and thyroid acropachy are most common. Periostitis in pachydermoperiostitis can be differentiated in that it is more florid, irregular and extends to the epiphyses while in thyroid acropachy there is a particular predilection for small bones of the hands and feet. Other causes include hypervitaminosis A, chronic venous insufficiency and diffuse idiopathic skeletal hyperostosis [1][5].