Tumour-induced osteomalacia: the long road to diagnosis and recovery.

Tumour-induced osteomalacia is caused by tumorous production of fibroblast growth factor 23 (FGF23) leading to urinary phosphate wasting, hypophosphataemia and decreased vitamin D activation. The resulting osteomalacia presents with muscle weakness and bone pain but progresses to multiple pathological fractures. Patients often remain undiagnosed for years with severe physical, psychological and economic ramifications. A young woman presented with multiple spontaneous fractures including bilateral femoral fractures. Laboratory tests revealed severe hypophosphataemia, elevated bone turnover markers and low to normal calcium and 25-hydroxy-vitamin D levels. Treatment with phosphate, alfalcalcidol, calcium and magnesium was initiated. 68Gallium-DOTATOC positron emission tomography imaging revealed a mass in the right foot and venous sampling of FGF23 from all extremities confirmed this tumour as the culprit. Biopsy and histology were consistent with a phosphaturic mesenchymal tumour, which was surgically resected. Phosphate levels quickly normalised postoperatively but a long convalescence with hungry bone syndrome, fracture healing and physical therapy followed.

Adrenocorticotropic hormone-secreting phaeochromocytoma as a cause of treatment-resistant hypertension and recurrent pulmonary emboli.

We report an unusual case of a patient presenting with Cushing's syndrome caused by a phaeochromocytoma secreting adrenocorticotropic hormone (ACTH). The patient had a history of treatment-resistant hypertension, secondary amenorrhoea and tendency towards hypokalaemia. She had multiple signs of Cushing's syndrome, such as swelling, bruising, abdominal striae and proximal myopathy. Hypokalaemia is more common in patients with ectopic ACTH-secretion than other causes of Cushing's syndrome. Computed tomography, adrenal vein sampling and biochemistry could confirm an ACTH-secreting phaeochromocytoma. It is important to consider that hypersecretion of more than one hormone may exist in a unilateral adrenal adenoma. This patient also presented with recurrent pulmonary emboli, and there is an increased risk of venous thromboembolism in patients with ACTH-secreting phaeochromocytoma. Anticoagulation should be considered for as long as the disease is active. We demonstrate that unilateral adrenalectomy can be curative in patients with ACTH-secreting phaeochromocytoma.

HNF1B variant without hyperglycaemia as a cause of isolated profound hypomagnesaemia.

A young man presented unconscious with severe hyponatraemia, hypokalaemia, hypomagnesaemia and metabolic alkalosis. After 4 months of treatment in hospital, the hypomagnesaemia persisted. The patient had no signs of diabetes mellitus, and radiology showed no abnormalities of the kidneys, pancreas or genitourinary tract. A parenteral magnesium load demonstrated renal wasting with increased fractional urinary excretion of magnesium. Genetic tests for Gitelman as well as Bartter syndromes were negative. However, a wider genetic panel revealed that the patient was heterozygous for a deletion on chromosome band 17q12, encompassing the whole HNF1B gene.This case highlights the importance of considering pathogenic HNF1B variants in isolated profound hypomagnesaemia caused by renal wasting. Pathogenic HNF1B variants may partly mimic hypomagnesaemia found in Gitelman and Bartter syndromes and may be present without other features linked to HNF1B variants, including diabetes mellitus.