29 — Parathyroid Disease, Calcium Regulation and Neuropsychiatric Symptoms
Series: Endocrine Origins of Psychiatric Symptoms
Evidence class: Established medical association; mechanisms and effect sizes variable

Abstract
Parathyroid hormone governs calcium and phosphate homeostasis through its actions on kidney, bone and indirectly the intestine. Primary hyperparathyroidism can produce a spectrum of neuropsychiatric complaints ranging from fatigue and impaired concentration to mood disturbances and, rarely, psychosis. It provides a concrete example of mineral physiology influencing mental status, while illustrating the difficulty of attributing nonspecific symptoms to an endocrine abnormality.

The calcium signal
Altered calcium physiology affects neuromuscular function and neural excitability. Primary hyperparathyroidism often produces elevated calcium or a characteristic PTH–calcium relationship, but presentations and severity vary widely. Some patients have kidney stones, bone disease, gastrointestinal symptoms or changes in mood and cognition; others are asymptomatic. The coincidence of depression with mild biochemical hyperparathyroidism does not prove it is the cause of the depression.

Mechanisms beyond one ion
PTH itself, calcium changes, sleep disturbance, chronic discomfort, inflammatory signaling and coexisting illness may contribute to reported symptoms. Studies of psychiatric improvement after correction of parathyroid disease are difficult to interpret because outcomes and follow-up vary. Severe hypercalcemia can cause delirium, dehydration and major mental-status changes, which represent a different clinical category from long-standing depression with modest biochemical abnormalities.

Why this matters for the oxalate debate
The intestine can bind dietary oxalate with calcium without materially changing circulating calcium. Conversely, primary hyperparathyroidism may increase urine calcium and stone risk through systemic regulation. Calcium oxalate stone formation can therefore arise from high urinary calcium, high urinary oxalate, low urine volume or other factors. An individual with both kidney stones and psychiatric symptoms should not be assumed to have an oxalate-driven brain disorder when an independently testable parathyroid explanation may exist.

A clinically useful pathway
Appropriate evaluation of serum calcium, albumin or ionized calcium and PTH depends on context. Significant abnormalities call for endocrine interpretation; minor variants may not explain symptoms. The overarching goal is not indiscriminate laboratory hunting, but recognition of conditions where correction of a real endocrine process can alter health outcomes.

Conclusion
Parathyroid disease demonstrates the possibility of metabolic and endocrine psychiatric manifestations. It also provides a warning: a shared mineral—calcium—does not make two distinct disorders causally identical.

Selected readings
- A Clinical Review of the Psychiatric Sequelae of Primary Hyperparathyroidism: https://pmc.ncbi.nlm.nih.gov/articles/PMC8549683/