Atypical Femur Fracture Unmasking Follicular Thyroid Cancer in a 54-year-old Woman

Case Presentation

A 54-year-old woman presented to the endocrinology clinic after sustaining an atypical fracture to her left lesser trochanter. She was sitting in her car in the driveway when her husband unintentionally surprised her by appearing in the window. She pushed forcefully on the brake pedal and felt a crack. She experienced immediate severe pain in the left hip area. She went to the emergency room, where an x-ray was performed (Fig. 1). Hip magnetic resonance imaging showed a hyperintense intertrochanteric soft tissue mass of the left hip (Fig. 2), and biopsy of this mass revealed crowding, elongated/enlarged nuclei, nuclear grooves, and scattered intranuclear pseudoinclusions (Fig. 3). Her medical history was significant for a 5.2-cm thyroid follicular adenoma removed in 2014 and gastric acid reflux. The patient reported little to no pain with ambulation and no night pain symptoms. Physical examination was unremarkable with normal gait, no joint/muscle tenderness, and normal range of hip motion.

Fig. 1.

X-ray of the left hip showing avulsion fracture (arrow) at the left lesser trochanter.

Fig. 2.

Magnetic resonance imaging of the left femur showing a signal intensity near the left lesser trochanter with cortical disruption (arrow).

Fig. 3.

High-power hematoxylin and eosin staining highlighting nuclear features of papillary thyroid cancer including cytologic crowding, elongated/enlarged nuclei, nuclear grooves, and scattered intranuclear pseudoinclusions.

What is the diagnosis?

Answer

Follicular thyroid cancer (FTC) metastasized to the bone. FTC is the second most common thyroid cancer and is known to metastasize hematogenously rather than through the lymphatic system, which could explain its more common spread.¹ FTC usually presents with distant metastasis rather than local metastasis. The incidence of distant metastasis in FTC is approximately 6% to 20%, with bones and lungs being the most common sites.² Outcomes for patients with metastatic FTC are poor, with a 10-year survival of 41% among those with metastatic disease at the time of diagnosis.³ This patient was further evaluated after undergoing a bone biopsy of the left lesser trochanter lesion that revealed FTC. On thyroid ultrasound, she had 2 nodules in her remaining thyroid gland (a 0.9-cm isthmus nodule and a 0.7-cm right lower nodule). Both were biopsied, and the isthmus nodule was suspicious for malignancy, but the right nodule was benign. She underwent completion thyroidectomy with bilateral and central neck dissection, and pathology revealed a 0.6-cm papillary thyroid cancer (follicular variant) with negative lymph nodes. The histology from the initial surgery in 2014 was reviewed and confirmed thyroid follicular adenoma.

Imaging studies performed prior to her treatment with iodine-131 showed that she also had a right parietal bone lesion and lung nodules. She underwent iodine-131 therapy and intravenous zoledronic acid administration without prophylactic left hip fixation. Her serum thyroglobulin level has decreased but remains detectable. This case highlights the importance of thorough investigation of a metastatic lesion because this may lead to early diagnosis and appropriate management of FTC.

Disclosure

The authors have no multiplicity of interest to disclose. Patient consent was obtained. The views expressed in this article are those of the authors and do not reflect the official policy of the Department of Army/Navy/Air Force, Department of Defense, or the U.S. Government.