Exploring Thyrotoxic Hypercalcaemia Through Two Cases: A Myriad of Uncertainties

Hypercalcaemia is a recognised complication of thyrotoxicosis usually related to increased bone resorption. However, coexistent hyperphosphataemia is uncommon and may create diagnostic uncertainty. It is postulated that serum calcium and phosphate levels rise due to high bone turnover and increased renal reabsorption of phosphate in response to excess thyroxine. Hypercalcaemia may also alter the clinical presentation of thyrotoxicosis, making both diagnosis and management challenging. We report two patients with this unusual biochemical presentation. The first patient was a 69-year-old woman who presented with body aches, lethargy, low mood, constipation, polyuria, and proximal muscle weakness for 2 months. The second was a 56-year-old woman who presented with palpitations, anxiety, tremulousness, dyspnoea, dysphagia, and headache for 4 months. Both had multinodular goitres (MNGs) without eye disease. Their TSH levels were undetectably low with extremely high free T4 levels. Serum calcium and phosphate levels were high in both patients. ALP levels were mildly elevated, vitamin D levels were deficient or insufficient, and parathyroid hormone (PTH) levels were low-normal. DXA scans revealed severe osteoporosis. Both patients improved clinically and biochemically with adequate intravenous hydration, frusemide, carbimazole, propranolol, and bisphosphonates. The second patient underwent a successful left thyroid lobectomy, while the first patient remained well on medical treatment. Unexplained hypercalcaemia and hyperphosphataemia should alert the clinicians to the possibility of underlying thyrotoxicosis. Prompt recognition and management is essential to prevent bone loss, correct metabolic abnormalities, and avoid complications. Clinicians should also consider the possibility of hypercalcaemia associated with thyroid dysfunction in patients presenting with nonspecific symptoms such as fatigue, constipation, proximal weakness, polyuria, or mood changes.