Is your Calcium Level Elevated due to a Problem with your Parathyroid Gland?
Sean D. Houston, M.D.
Calcium is the most common mineral in the body. The average human body contains approximately 1,000 grams of elemental calcium. The majority of this (over 99%) is found in bone. Calcium is important in mediating both subcellular, as well as extracellular functions. The average human diet requires 500 mg per day and calcium levels are modified by absorption in the gut (the duodenum and upper jejunum) as well as absorption and excretion in the kidney. Your calcium blood level is monitored and adjusted on a second to second basis by a coordinated symphony of endocrinologic factors throughout your body. Vitamin D is responsible for calcium absorption in the gastrointestinal tract where parathyroid hormone modulates calcium levels by working primarily on the kidney and in the bones.
Over 90% of patients who have elevated calcium levels and normal kidney function have primary hyperparathyroidism. Primary hyperparathyroidism is due to parathyroid over secretion of PTH (parathyroid hormone) because a parathyroid gland (or less commonly more than one of the glands) has become insensitive to the normal inhibitory feedback loop that would typically "kick in" when calcium levels in your blood reached appropriate levels. Your medical doctor, prior to sending you to the Ears, Nose, and Throat surgeon, may have done a directed history/physical and blood work to rule out less common sources of elevated calcium levels (hypercalcemia).
Sources of Elevated Calcium Levels Unrelated to Your Parathyroid
Overuse of Thiazide Diuretics
Excessive Intake of Calcium
Excessive Intake of Vitamin A and D
Excessive Muscular Damage (calcium is released by damaged muscle cells)
Excessive Immobilization (secondary to high bone turnover)
Your primary care physician can usually diagnose these problems. However if your calcium levels are elevated and your parathyroid hormone levels are on the high side, you most likely have a parathyroid adenoma. Consistent PTH levels of only 30-35 ng/L (normal range 15-55 ng/L) can be diagnostic of 1° hyperparathyroidism if your calcium levels are high at the same time. Primary hyperparathyroidism occurs rarely across the entire population but is more common in women and is seen more often in people older than 50 years old. Twenty-eight out of every 100,000 people are diagnosed with this disease and 100,000 new cases are diagnosed in the United States every year.
Historically symptoms of prolonged elevated calcium levels secondary to 1° hyperparathyroidism are recurrent kidney stone formation, bone fracture, intestinal absorption problems and mental status changes. These are classically remembered as "stones, bones, groans (GI), and moans (psychiatric). The truth is, however, today these are rarely seen as presenting symptoms in the western hemisphere. Most commonly 1° hyperparathyroidism is picked up on routine blood work before these symptoms have a chance to develop. Asymptomatic patients do often have evidence of reduced cortical bone in their axial bones (clear evidence of reduction in the distal forearm and femoral neck has been documented, where data suggesting decreased bone density in the hip and spine is more controversial). Patients often will complain of fatigue, weakness, apathy and mood swings. Psychiatric symptoms are characteristically seen in older patients with higher calcium levels and a liberal attitude has been advocated toward parathyroid surgery in the elderly with psychiatric symptoms and the appropriate blood work to suggest primary hyperparathyroidism. The most common presenting manifestation in symptomatic hyperparathyroidism is renal stones and is an undisputed indication for parathyroid exploration.
Over 85% of people who undergo parathyroid exploration have a solitary adenoma as a source of their elevated calcium. It is very unusual for hypercalcemia to be due to more than one adenoma/abnormality of the parathyroid gland. Multiple adenomas occur in only 1-2% of cases. Malignancy is even less common of the parathyroid glands occurring in just less than 1% of cases. Today more than 95% of patients are cured at initial exploration performed by an experienced surgeon. Radiologic developments like Tc99m sestamibi scanning pre-operatively have helped localize the offending parathyroid gland so that parathyroid exploration can be more directed and minimally invasive without increasing the risk of surgical complication. Minimally invasive surgery not only allows for a smaller incision than the classic bilateral neck dissection required for 4 gland exploration but also can reduce the total operative time under anesthesia. Directed minimally invasive parathyroid surgery has the advantage of reducing the risk of recurrent laryngeal nerve injury and the risk of postoperative hypocalcemia because no dissection is performed on the side opposite the localized adenoma.
Variability in the location, size, shape and number of parathyroid glands requires a thorough understanding of parathyroid embryology and anatomy. Although most patients have four parathyroid glands, 5% of the population will have more than four. A normal parathyroid gland is only 3-4 mm long and weighs 30-50 mg. They are classically yellow to tan-brown. But the size, shape and appearance of a parathyroid adenoma are highly variable. The superior and inferior parathyroid glands arise embryologically from different structures. This and the longer migration of the inferior glands from their place of origin results in a greater variability in their location. However, an experienced surgeon, like those found at Coastal Ear, Nose and Throat
armed with a detailed knowledge of the anatomy and the highly variable possibilities frequently encountered in endocrinologic surgery can most likely effect a successful outcome.
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