Case 328: Brown Tumor in Hyperparathyroidism Due to Parathyroid Adenoma.

A 45-year-old female patient with diffuse osteoarticular pain, particularly low back pain, was referred by a rheumatologist for an updated radiologic evaluation. The patient had experienced these symptoms for many years and was diagnosed with human leukocyte antigen B27-negative spondyloarthritis approximately 11 years prior, based on findings of bilateral erosive sacroiliitis at pelvic radiography and bone scintigraphy with technetium 99m (99mTc) methylene diphosphonate. After 3 years of treatment with a tumor necrosis factor-α inhibitor (adalimumab), which was effective for pain, the patient was lost to follow-up. At the current presentation, approximately 8 years after being lost to follow-up, the patient presented with worsening low back pain. The presence of nonobstructing kidney stones on US images confounded the underlying cause of worsening pain. The patient also experienced fatigue and depressed mood. Routine blood tests revealed a normal blood cell count, creatinine level of 0.64 mg/dL (56.58 μmol/L) (normal range, 0.30-1.1 mg/dL [26.52-97.24 μmol/L]), C-reactive protein level of 1.1 mg/dL (normal, <1 mg/dL), and vitamin D level of 21 ng/mL (52.42 nmol/L) (normal range, 30-100 ng/mL [74.88-249.60 nmol/L]). Noncontrast MRI of the thoracic and lumbar spine, MRI of the sacroiliac joints, and CT of the abdomen and pelvis were performed.