Introduction: Cardiovascular manifestations of hypocalcaemia include reversible CHF, prolonged QTc and ventricular arrhythmias. In patients presenting with hypocalcaemia, diagnosis of hypoparathyroidism is straightforward, but determining its cause is challenging.
Case Report: 33 year lady admitted (23 November 2018) with VF arrest. Bloods showed low calcium (1.62 mmol/l), magnesium (0.48 mmol/l) and potassium (2.3 mmol/l) and ECG showed prolonged QTc. PTH were inappropriately normal (2.4 pmol/l) and vitamin D low (34 nmol/l). Phosphate were normal (0.82 mmol/l) and eGFR >90. Parathyroid antibodies were negative. She had circumoral and finger tip paraesthesia/numbness in preceding two weeks. No evidence of gastrointestinal loss (diarrhoea, vomiting, PPI, coeliac disease, alcoholism or eating disorder) or renal loss (diuretics, recent AKI, abnormal urinalysis, or post-obstructive nephropathy). Menstrual cycles were regular. She was investigated earlier for iron deficiency anaemia with negative coeliac screen. No family history of electrolyte imbalance, sudden cardiac death, endocrine or autoimmune diseases. She was treated with intravenous magnesium and calcium. Potassium levels were normal except on arrival. Calcium and magnesium levels remained resistant to correction until alfacalcidol was started, within few days of which both levels were stabilised without supplementation. Levels on 31 May 2019: calcium 2.38 mmol/l and magnesium 0.7 mmol/l (on alfacalcidol 1 (g only). QTc prolongation occurs in hypocalcaemia, hypomagnesemia or hypokalemia. Arrhythmias occur when levels are significantly low (calcium <1.9 mmol/l, magnesium <0.4 mmol/l or potassium <2.5 mmol/l). In this case, hypocalcaemia might have caused VF arrest. Hypocalcaemia with high PTH occurs in vitamin D deficiency & CKD; hypocalcemia with low/low-normal PTH occurs in hypomagnesemia (PTH resistance) and hypoparathyroidism. With no history of neck surgery/irradiation/infiltrative/autoimmune diseases, a diagnosis of primary hypoparathyroidism is considered. Autoimmune hypoparathyroidism is still a possibility, as positive autoantibodies occur only in 25% of autoimmune hypoparathyroidism.
Conclusion: Most hypoparathyroidism patients present with paresthesia, cramps or tetany. However, rarely they can present with arrhythmias, seizures or bronchospasm/laryngospasm.