How does hyperparathyroidism cause constipation?

Mechanism of Constipation in Hyperparathyroidism

Hyperparathyroidism causes constipation primarily through hypercalcemia, which reduces neuromuscular excitability in the gastrointestinal tract, leading to decreased intestinal motility. 1

Pathophysiological Mechanism

Hyperparathyroidism leads to constipation through several interconnected mechanisms:

1. Elevated Calcium Levels:

   • Hypercalcemia directly reduces neuromuscular excitability in the gastrointestinal tract 1
   • This decreased excitability results in reduced intestinal peristalsis and slower transit time
   • The severity of constipation often correlates with the degree of hypercalcemia 2

2. Types of Hyperparathyroidism Associated with Constipation:

   • Primary hyperparathyroidism (most common cause of hypercalcemia) 3
   • Tertiary hyperparathyroidism (after longstanding secondary hyperparathyroidism) 4
   • Malignancy-associated hyperparathyroidism 5

3. Clinical Presentation:

   • Constipation is one of the most common gastrointestinal manifestations of hyperparathyroidism 1
   • It may be present even in mild hypercalcemia (total calcium <12 mg/dL) 2
   • Approximately 20% of patients with mild hypercalcemia experience constitutional symptoms including constipation 2

Clinical Significance and Management

The American Gastroenterological Association recognizes hypercalcemia as one of the metabolic disturbances that can cause secondary constipation 5. Management should focus on treating the underlying hyperparathyroidism:

1. Diagnosis:

   • Measure serum calcium, phosphorus, and PTH levels 5
   • Distinguish between primary hyperparathyroidism (elevated or normal calcium with inappropriately elevated PTH) and other causes 6

2. Treatment Options:

   • Parathyroidectomy: Indicated for symptomatic patients, including those with persistent constipation 5, 6
   • Medical Management:
     • Optimize vitamin D levels (target >20 ng/mL) 6
     • Ensure adequate hydration 2
     • Consider cinacalcet for severe hyperparathyroidism when surgery is not an option 6

3. Monitoring:

   • Regular assessment of calcium, phosphorus, and PTH levels based on severity of disease 6
   • Follow-up of gastrointestinal symptoms after treatment

Important Considerations

• Constipation may persist even after correction of hypercalcemia due to established patterns of bowel dysfunction 1
• In pediatric patients with hyperparathyroidism, persistent constipation ("stipsis") is particularly noted with calcium levels >12 mg/dL 7
• Distinguishing constipation due to hyperparathyroidism from other causes is important for appropriate management 5

Treatment Response

Constipation often improves following successful treatment of hyperparathyroidism, particularly after parathyroidectomy in appropriate candidates 1. This improvement in gastrointestinal symptoms supports the direct pathophysiological link between elevated calcium levels and reduced intestinal motility.

In summary, the primary mechanism by which hyperparathyroidism causes constipation is through hypercalcemia-induced reduction in neuromuscular excitability in the gastrointestinal tract, leading to decreased intestinal motility and slower transit time.