Related Subjects:
|Calcium Physiology
|Calcitonin
|Hypocalcaemia
|Hypercalcaemia
|Hypomagnesaemia
|Hypermagnesaemia
|Primary Hyperparathyroidism
|Familial hypocalciuric hypercalcaemia (FHH)
|Sarcoidosis
⚠️ Key: Always distinguish Familial Hypocalciuric Hypercalcaemia (FHH) from Primary Hyperparathyroidism (PHPT).
Parathyroidectomy does not correct calcium in FHH → misdiagnosis can lead to unnecessary surgery.
🧾 About Familial Hypocalciuric Hypercalcaemia (FHH)
- Autosomal dominant condition → lifelong mild hypercalcaemia.
- Characterised by ⬆️ serum calcium, ⬆️/normal PTH, and ⬇️ urinary calcium.
- Often picked up incidentally; patients usually asymptomatic.
🧬 Aetiology
- CASR gene mutations → loss of function in the calcium-sensing receptor.
- CASR normally regulates PTH secretion and renal calcium excretion.
- Mutation = parathyroid “thinks” calcium is low → keeps PTH inappropriately normal/high → mild hypercalcaemia.
- Genetic testing confirms diagnosis in uncertain cases.
🩺 Clinical Presentation
- Usually asymptomatic with incidental hypercalcaemia.
- Rare cases: chondrocalcinosis, pancreatitis.
- No typical PHPT features (stones, bones, abdominal groans, psychiatric moans).
🔎 Investigations
- Serum Calcium: Mildly elevated (≈2.6–3.0 mmol/L).
- PTH: Normal or slightly raised (inappropriately high for calcium level).
- Serum Magnesium: Often raised.
- Urinary Calcium: Low fractional excretion (<0.01), diagnostic hallmark.
- Urinary cAMP: Normal (vs elevated in PHPT).
⚖️ Differential Diagnosis
- PHPT: High calcium + high PTH but ⬆️ urinary calcium; can cause stones, osteoporosis.
- FHH: Mild calcium rise, ⬇️ urinary calcium, benign course.
💊 Management
- No treatment required: Benign course, lifelong monitoring only.
- Parathyroidectomy: Ineffective in FHH (contrast with PHPT).
- Family screening: Hypercalcaemia in relatives strongly suggests FHH.
📌 Distinguishing FHH vs PHPT
| Feature | FHH | PHPT |
|---|
| Age of onset | Often young, familial | Middle-aged/older |
| Serum calcium | Mild ↑ (stable) | ↑ (often progressive) |
| PTH | Normal/↑ (inappropriate) | ↑ |
| Urinary calcium | Low | Normal/↑ |
| Clinical features | Usually asymptomatic | Stones, bones, GI + psych symptoms |
| Family history | Often +ve | Usually sporadic |
| Effect of parathyroidectomy | No effect | Cures |
