# Hypoparathyroidism and Pseudohypoparathyroidism

> Hypoparathyroidism and pseudohypoparathyroidism for NEET-PG Medicine: tetany signs, PTH resistance, GNAS defects, Albright osteodystrophy and biochemistry.

- Canonical URL: https://prepelephant.com/topics/neet-pg/medicine/hypoparathyroidism-and-pseudohypoparathyroidism
- Exam / course: NEET-PG · Subject: Medicine
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-08
- Last updated: 2026-10-08
- Reference basis: Harrison's Principles of Internal Medicine; Williams Textbook of Endocrinology; Davidson's Principles and Practice of Medicine
- How to cite: "Hypoparathyroidism and Pseudohypoparathyroidism", PrepElephant, https://prepelephant.com/topics/neet-pg/medicine/hypoparathyroidism-and-pseudohypoparathyroidism

## Direct answer

Hypoparathyroidism is deficient parathyroid hormone secretion, producing hypocalcaemia, hyperphosphataemia and a low or inappropriately normal PTH. Pseudohypoparathyroidism is target-organ resistance to PTH, so calcium and phosphate look the same but PTH is raised. The biochemical pair separates them, and post-thyroidectomy hypoparathyroidism is the commonest true cause.

## What you must remember

- **Tetany signs:** Chvostek sign (facial twitch on tapping the facial nerve) and Trousseau sign (carpopedal spasm after cuff inflation above systolic pressure) show neuromuscular irritability from low ionised calcium.
- **Causes of true hypoparathyroidism:** neck surgery, autoimmune disease including APS type 1, DiGeorge syndrome, infiltrative disease, and severe hypomagnesaemia, which blocks PTH release.
- **Biochemistry of hypoparathyroidism:** low calcium, high phosphate and low or inappropriately normal PTH.
- **Pseudohypoparathyroidism:** PTH resistance from GNAS (Gs alpha) defects, with high PTH despite hypocalcaemia and hyperphosphataemia.
- **Albright hereditary osteodystrophy:** short stature, round face, shortened fourth and fifth metacarpals, obesity, subcutaneous ossifications and variable intellectual disability.
- **Pseudopseudohypoparathyroidism:** the AHO phenotype with normal calcium and PTH, because the GNAS defect is inherited on the paternal allele and renal resistance does not develop.
- **Confirmation:** the Ellsworth-Howard test, with PTH infusion and measurement of urinary cAMP and phosphaturia, is blunted in pseudohypoparathyroidism type 1a.

## Worked example: cramps after a thyroid operation

A 32-year-old woman, five years after total thyroidectomy, presents with perioral tingling and carpopedal spasm. Chvostek sign is positive. Her corrected calcium is low, phosphate is high and PTH is low, which points to hypoparathyroidism.

1. **Check magnesium:** Serum magnesium is measured, because low magnesium impairs PTH release and action.
2. **Check vitamin D:** 25-hydroxyvitamin D is measured to exclude a coexisting deficiency.
3. **Check the heart:** An ECG looks for QT prolongation, the arrhythmia risk in hypocalcaemia.
4. **Start treatment:** Oral calcium is given with an active vitamin D analogue such as calcitriol or alfacalcidol, titrated to low-normal calcium to limit hypercalciuria and renal stones.

Contrast this with a six-year-old boy who is short, has a round face and shortened fingers, and whose calcium is low with a raised PTH and raised phosphate. Here the picture is pseudohypoparathyroidism. Checking TSH is worthwhile, since thyroid stimulating hormone resistance is common in the same disorder, and the family history is examined because parental transmission determines whether renal resistance develops.

## Where the examiner separates the two

The stem almost always gives calcium and asks for PTH.

- **Trap:** reading a raised PTH as hypoparathyroidism. — **Correct:** a high PTH means pseudohypoparathyroidism, vitamin D deficiency or chronic kidney disease, so phosphate and vitamin D levels must be read alongside it.
- **Trap:** equating Albright features with one diagnosis. — **Correct:** Albright features with normal calcium indicate pseudopseudohypoparathyroidism, while the same features with hypocalcaemia indicate type 1a.
- **Trap:** treating Chvostek and Trousseau signs as diagnostic. — **Correct:** both simply reflect low ionised calcium and are not diagnostic of pseudohypoparathyroidism.
- **Trap:** missing chronic hypocalcaemia as a clue. — **Correct:** it can produce subcapsular cataracts and basal ganglia calcification, which examiners sometimes use as the distinguishing clue.

## Frequently asked questions

### Which hormonal result separates hypoparathyroidism from pseudohypoparathyroidism?

A low or inappropriately normal PTH with hypocalcaemia and hyperphosphataemia points to hypoparathyroidism. A raised PTH with the same calcium and phosphate changes points to pseudohypoparathyroidism, where the parathyroid glands respond but target organs do not.

### What are the classic signs of tetany on examination?

Chvostek sign, a facial twitch on tapping the facial nerve in front of the ear, and Trousseau sign, carpopedal spasm after blood pressure cuff inflation, are the classic signs of neuromuscular irritability from hypocalcaemia. Both can be absent in mild cases.

### Which features make up Albright hereditary osteodystrophy?

Albright hereditary osteodystrophy includes short stature, round face, brachydactyly with shortened metacarpals and metatarsals, obesity and subcutaneous ossifications. It is seen in pseudohypoparathyroidism and in pseudopseudohypoparathyroidism, which differs by having normal calcium and PTH.

### What is the Ellsworth-Howard test used for?

The Ellsworth-Howard test measures urinary cAMP and phosphate excretion after an infusion of PTH. In pseudohypoparathyroidism type 1a the response is blunted, which confirms renal resistance to parathyroid hormone.

### Why is calcium given with calcitriol in hypoparathyroidism?

Calcium with calcitriol is used in hypoparathyroidism because the body cannot make enough active vitamin D without PTH to raise intestinal calcium absorption. Calcitriol or alfacalcidol replaces that action, and calcium is titrated to avoid hypercalciuria.