Marjorie A. Thurlow, MSIV, Gregory Carney, MD, and George B. Greenfield, MD

April 17, 2002

Answer

3. Hypertrophic osteoarthropathy

Hypertrophic osteoarthropathy (HOA) is a clinical syndrome consisting of digital clubbing, extremity hypertrophy secondary to osseous proliferation, arthralgias secondary to synovial involvement, and autonomic dysfunction. It would be rare to encounter all of these signs and symptoms in a single patient. In standard case scenarios, the HOA patient complains of a burning or aching pain in the ankles, wrists, or knees. The pain is worse when the patient is recumbent, and it remits with limb elevation. However, the patient may also present with paresthesias, flushing, and diaphoresis.

HOA has commonly been associated with intrathoracic neoplasms and chronic infections. For this reason, most thoracic literature specifically refers to this syndrome as pulmonary hypertrophic osteoarthropathy (PHO). However, the umbrella term "HOA" is becoming more commonplace in radiologic literature because the radiographic patterns of HOA may be associated with nonpulmonary processes. For example, HOA has been noted in cyanotic congenital heart dis-ease, cystic fibrosis, inflammatory bowel disease, cirrhosis, and pachydermoperiostitis, the rare autosomal dominant disorder. While multiple etiologies are possible, a clinician who suspects the presence of HOA should investigate the possibility of a pulmonary neoplasm. In approximately 80% of cases, the cause of secondary HOA has been identified as bronchogenic carcinoma. Rosenthall and Kirsch [1] maintain that the HOA incidence in patients with bronchogenic carcinoma is nearly 10%.

For assistance in making the clinical diagnosis of HOA, the clinician may turn to such studies as radiographic plain films and radionuclide bone scans. On plain film, a diffuse ossifying periostitis of the distal diaphyses of multiple long bones may be present. HOA is unusual in that it often involves both the upper and lower extremities but rarely affects the axial skeleton or distal phalanges. With regard to any single bone, periostitis may extend to the metaphysis but generally eschews the epiphysis. HOA may also show linear periosteal bone formation. With accumulation, this ossification may give the affected diaphysis a thicker, denser, undulating appearance.

Because of their greater sensitivity, radionuclide bone scans provide a more accurate picture of HOA at an earlier stage. However, the clinician typically orders such a study once a plain radiograph has already reinforced suspicions of HOA. This is done to prevent confusion of HOA with possible metastatic disease to the skeleton.

On radionuclide bone scans, HOA appears in the shafts of affected long bones as a symmetrical pattern of diffusely increased uptake along the diaphyseal cortices. In more advanced stages, this pattern resembles "parallel tracks" that likely represent either hyperemia accompanying the periosteal inflammatory reaction or increased osteoblastic activity. Concurrent synovitis may also be observed if there is periarticular involvement.

It is generally believed that treatment of the underlying condition results in resolution of the signs and symptoms of secondary HOA. The following etiologies for secondary HOA have been proposed, but none is universally embraced: release of vasodilators, increased anteriovenous shunting, reflex peripheral vasodilation secondary to vagal activity, and the interplay of estrogen, growth hormone, and prostaglandins. Notably, Sagar et al [2] have suggested that although multiple treatments correlate with clinical and radiographic improvement of secondary HOA, spontaneous remission may be a possible common denominator underlying such therapeutic success.

In summary, plain radiographic films and radionuclide bone scans may aid the clinician in making the diagnosis of HOA. The clinician must make a diagnosis based on integrating information from studies with clinical findings. When the primary condition underlying HOA is addressed, both radiologic and clinical findings tend to regress.

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