Secondary hyperparathyroidism

Secondary hyperparathyroidism (SHPT) is elevation of parathyroid hormone (PTH) secondary to hypocalcemia.

PTH maintains calcium homeostasis by acting on the renal tubules, on calcium stores in the skeletal system, and indirectly on the gastrointestinal tract through activation of vitamin D and enteral absorption.

The disease most frequently associated with SHPT is chronic kidney disease. However, the most common reason for SHPT is vitamin D deficiency. Inadequate vitamin D stores are common in older people, those with malabsorption syndromes, or those with limited exposure to sunlight.

Management includes appropriate treatment of the underlying cause and vitamin D supplementation. Parathyroidectomy is infrequently required to remove irreversibly enlarged parathyroid glands in an effort to restore normal parathyroid physiology.

Untreated, it can result in significant skeletal and cardiovascular complications, which contribute to overall morbidity and mortality.

Any disorder that results in hypocalcemia will elevate parathyroid hormone levels and can serve as a cause of secondary hyperparathyroidism (SHPT). The most frequent causes are chronic kidney disease (CKD), malabsorption syndromes, and chronic inadequate sunlight exposure, acting via alterations in vitamin D, phosphorus, and calcium.

SHPT is a complication of CKD and is important in the pathogenesis of CKD-mineral bone disorder (MBD). CKD-MBD is defined as a systemic disorder of mineral and bone metabolism due to CKD manifested by either one or a combination of the following: abnormalities of calcium, phosphorus, PTH, or vitamin D metabolism; abnormalities in bone turnover, mineralization, volume, linear growth, or strength; vascular or other soft tissue calcification.[1]Kidney Disease: Improving Global Outcomes (KDIGO) clinical practice guideline. Diagnosis, evaluation, prevention, and treatment of chronic kidney disease-mineral and bone disorder (CKD-MBD). 2009; selective update 2017 [internet publication]. https://kdigo.org/guidelines/ckd-mbd