Mechanism of acute lower extremity pain syndrome in fluoride-treated osteoporotic patients.

Acute pain in the lower extremity, which has previously been attributed to synovitis or fasciitis, develops in about 15 percent of osteoporotic patients treated with sodium fluoride. This report describes 11 osteoporotic women in whom this syndrome developed while they were being treated with sodium fluoride (mean dose 78 mg per day; range, 60 to 90). [99mTc]Hydroxymethylene diphosphonate scintiscanning showed an increased number of foci of abnormal uptake in the lower extremities (p less than 0.05), when compared with results of scintiscanning in 12 nonsymptomatic osteoporotic women treated with sodium fluoride and 12 osteoporotic women treated with oral calcium carbonate only. The increased uptake was not restricted to the areas of pain. Roentgenography revealed stress microfractures in five of the 11 symptomatic patients. It is concluded that the acute lower extremity pain syndrome during fluoride therapy usually results from intense regional bone remodeling, which may be complicated by stress microfractures.