Brown tumors, also termed osteitis fibrosa cystica, are bone lesions resulting from prolonged hyperparathyroidism. They are not true tumors but rather localized bone changes due to excessive bone resorption and secondary fibrosis. The name “brown tumor” arises from the brownish color of the lesions, which is attributed to the buildup of hemosiderin, a pigment from hemorrhage, and the breakdown of red blood cells.
The term “brown tumor” was first used in the early 20th century to describe a kind of bone lesion connected with hyperparathyroidism. These lesions were observed in patients with primary hyperparathyroidism, a condition where excessive parathyroid hormone levels lead to abnormal calcium metabolism and bone changes.
Causes
Brown tumors are primarily connected with conditions that lead to prolonged or excessive secretion of parathyroid hormone, resulting in disrupted bone metabolism. The main causes include:
Primary Hyperparathyroidism
It is the most common cause of brown tumors. It happens when one or multiple of the parathyroid glands become active and produce over PTH. This hormone increases bone resorption, leading to the formation of brown tumors.
Secondary Hyperparathyroidism
It results from chronic kidney disorder or other conditions that cause low calcium levels in the blood. The body compensates by increasing PTH production. The persistent high PTH levels can cause bone changes similar to those seen in primary hyperparathyroidism, including brown tumors.
Tertiary Hyperparathyroidism
This occurs when the parathyroid glands become overactive after long-standing secondary hyperparathyroidism, even after the initial cause (like chronic kidney disease) is treated. The parathyroid glands continue to secrete excess PTH, leading to bone abnormalities including brown tumors.
Multiple Myeloma
Although not a direct cause, multiple myeloma can cause bone lesions that might be mistaken for or overlap with brown tumors. This condition involves abnormal plasma cells in the bone marrow that can cause bone destruction and may complicate the clinical picture.
Paget’s Disease of Bone
In uncommon cases, brown tumors can also be associated with Paget’s disease, a chronic bone disorder that involves abnormal bone remodeling. While not a primary cause, Paget’s disease can contribute to similar bone changes.
Other Rare Conditions
Certain other uncommon conditions that lead to bone resorption or altered calcium metabolism may also be connected with brown tumors. However, these are less common and usually involve complex or multiple factors.
Symptoms
Brown tumors often present with symptoms related to the underlying condition causing excessive parathyroid hormone secretion rather than the tumors themselves.
Patients may experience generalized bone pain, swelling, or sensitivity in areas where the tumors are located. These symptoms are usually found in the bones of the hands, wrists, and jaw, though they can occur in other skeletal regions as well.
In some cases, the lesions might cause bone deformities or lead to fractures due to weakened bone structure.
Since brown tumors are usually a secondary effect of prolonged hyperparathyroidism, patients may also exhibit symptoms associated with hyperparathyroidism, like kidney stones, frequent fatigue, urination, and gastrointestinal disturbances.
The tumors may be discovered incidentally on X-rays or other imaging studies conducted for unrelated issues. As the underlying hyperparathyroidism is managed, the symptoms related to brown tumors often improve, and the lesions may slowly resolve.
Treatment
The main treatment for brown tumors involves addressing the underlying cause of excessive parathyroid hormone secretion. In cases of primary hyperparathyroidism, this often means surgical intervention to remove the overactive parathyroid glands. This approach can assist in normalizing PTH levels and subsequently reduce or eliminate the brown tumors.
For secondary hyperparathyroidism, treatment focuses on managing the underlying condition, like chronic kidney disease, and may include medicines or dietary adjustments to regulate calcium and phosphorus levels.
In addition to treating the primary condition, supportive measures may be employed to manage symptoms related to brown tumors. Pain management, physical therapy, and, in some cases, localized treatments like calcitonin or bisphosphonates can help alleviate discomfort and improve bone health.
As the underlying hyperparathyroidism is controlled and PTH levels return to normal, the brown tumors usually regress and resolve over time, leading to improved bone structure and function. Regular follow-up with imaging studies and laboratory tests is essential to observe progress and ensure effective treatment.
Why it occurs
Brown tumors occur mainly due to prolonged elevated levels of parathyroid hormone, which leads to significant bone changes. The key mechanisms include:
- Excessive Bone Resorption: Elevated PTH levels stimulate osteoclasts, the cells responsible for breaking down bone tissue. This leads to excessive bone resorption, where bone is removed quicker than it can be replaced. The result is a loss of bone density and structural integrity.
- Fibrous Tissue Formation: As bone is reabsorbed, it is replaced by fibrous tissue and hemosiderin (a pigment from bleeding and the breakdown of red blood cells). This fibrous tissue accumulates in the affected bone areas, forming the characteristic brown tumors.
- Increased Vascularity: The resorption and replacement process also increases the blood supply to the affected bones, which can contribute to the characteristic brown color of the lesions due to hemorrhage and the presence of hemosiderin.
These changes are most commonly seen in conditions like primary hyperparathyroidism, secondary hyperparathyroidism (often due to chronic kidney disease), and tertiary hyperparathyroidism. The tumors are not true neoplasms but rather reactive bone lesions resulting from these underlying disturbances in calcium and bone metabolism.
Diagnosis
Diagnosing brown tumors commonly involves a combination of imaging studies and laboratory tests. Initial detection often occurs through X-rays or CT scans, which reveal lytic bone lesions with well-defined margins, characteristic of brown tumors. These images help distinguish the lesions from other bone conditions.
Laboratory tests are crucial for confirming elevated parathyroid hormone (PTH) levels and assessing calcium and phosphorus metabolism, which indicate underlying hyperparathyroidism. In some cases, a biopsy may be performed to differentiate brown tumors from other bone pathologies and to confirm the diagnosis. Addressing the underlying hyperparathyroidism is essential for the effective management and resolution of the tumors.
Prevention
Preventing brown tumors primarily involves managing and addressing the conditions that lead to elevated parathyroid hormone levels. For individuals with the chance of primary hyperparathyroidism, regular observation, and early intervention can help identify and treat the condition before significant bone damage occurs.
In cases of secondary or tertiary hyperparathyroidism, effective management of underlying conditions like chronic kidney disease is important. This includes controlling calcium and phosphorus levels through medication, diet, and regular follow-up care. By managing these risk factors and conditions proactively, the development of brown tumors can be decreased, and overall bone health can be maintained.
Summary
Brown tumors, also known as osteitis fibrosa cystica, arise from prolonged elevated levels of parathyroid hormone, leading to excessive bone resorption and the formation of fibrous lesions. They are commonly associated with primary or secondary hyperparathyroidism. Diagnosis involves imaging studies and lab tests to assess PTH levels and bone metabolism, with biopsies sometimes needed to rule out other conditions.
Treatment focuses on addressing the underlying hyperparathyroidism through surgical or medical means, along with supportive measures for symptoms. Preventive strategies include managing conditions that cause elevated PTH and maintaining regular monitoring. Proper management can lead to the resolution of brown tumors and improved bone health.
