BACKGROUND: Thyroid acropachy is an extreme manifestation of autoimmune thyroid disease characterized by soft tissue swelling and periosteal bone changes, usually occurring in the fingers, toes, and lower extremities. Here, a patient with a distinctly unusual variant of thyroid acropachy is presented. PATIENT FINDINGS: The patient was a 48-year-old woman with Graves' disease and mild ophthalmopathy, who was euthyroid after treatment with Methimazole. Because of a persistently elevated serum alkaline phosphatase (ALP) with elevated bone fraction, a bone scan was performed. This showed increased uptake in the subcortical areas of the lower extremity bones. On questioning, she admitted to mild pain in her lower extremities. She had no other features of thyroid acropachy. Secondary causes of increased ALP, such as cancer, liver disease, and vitamin D deficiency, were excluded by appropriate tests. Therefore, and in view of the patient's underlying Graves' disease, a diagnosis of thyroid acropachy was made. SUMMARY AND CONCLUSIONS: Periosteal reaction in the long bones of the lower extremities is unusual in thyroid acropachy, and when it occurs, it is more likely to be associated with overt pain or prominent extrathyroidal manifestations of Graves' disease. This patient very likely had a variant of thyroid acropachy. This variant may be underreported because of its generally asymptomatic nature.