Investigating recurrent hypophostaemia

R. Agha-Jaffar; M. Reddy; D. Bassett; J. Cox

Oncogenic osteomalacia is a rare paraneoplastic phenomenon characterised by abnormal phosphate metabolism typically caused by discrete benign tumours. Due to the indolent presentation and slow progression, diagnosis is often delayed and localisation of the tumour can prove difficult. We present the case of a 64-years-old gentleman who was investigated by the endocrinology department for hypophosphataemia. Three years prior to this, he had started to experience exertional fatigue and myalgia. Within the same time frame, he sustained a minor injury to his ankle and later developed severe pain in the joint lasting several months. This was attributed to Looser zones on plain X-ray. He had no further significant medical history. Development and growth had been normal. Relevant results are tabulated. The low Tmp/GFR value confirmed renal phosphate wasting. In the context of a mildly elevated PTH level and inappropriately normal 1,25 (OH) Vitmain D/ FGF 23 levels, the hypophosphataemia was deemed consistent with oncogenic osteomalacia. Though CT images demonstrated low attenuation hepatic lesions, these were characterised as insignificant on MRI. No potential source was identified on functional imaging modalitites (octreotide scintigraphy, FDG-PET imaging or Ga68 DOTATATE PET). Symptomatic relief was gained with Sando Phosphate and alfcalcidol. Biochemical parameters normalised (fasting phosphate 0.77 mmol/l, ALP 117 μ/l) and a repeat bone scan showed full resolution in the areas of increased activity. Our case illustrates the difficulties in identifying tumours associated with this paraneoplastic phenomenon and how, despite unsuccessful localisation, medical therapy can be effective in the absence of definitive treatment.

Table 1
Variable	Values	Reference range
Fasting Phosphate Level	0.53 mmol/l	0.8–11.4 mmol/l
Corrected Calcium	2.24 mmol/l	2.15–2.60 mmol/l
Creatinine	100 mmol/l	75–114 mmol/l
Parathyroid Hormone Levels	14.6 pmol/l	1.1–6.8 pmol/l
Alkaline Phosphatase	255 μ/l	30–130 μ/l
25-OH Vitamin D	51.1 nmol/l	25–100 nmol/l
1–25(OH) Vit D	73 pmol/l	40–150 pmol/l
Fibroblast Growth Factor-23	63 RU/ml	<100 RU/ml
24 hour urinary phosphate excretion	20.73 mmol	16–48mmol
Fractional excretion of phosphate	14%
Tubular maximum for phosphate corrected for GFR (TmP/GFR)	0.35 mmol/l	0.89–1.34 mmol/l(corrected for age and gender)
Bone Scintigraphy	Multiple sites increased activity throughout skeleton with few small hot spots
Bone Mineral Density (DEXA) Scan	T4-L2: (T score) −2.7: Femoral neck: (T score) −1.7

Results:

Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Funding: This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.

Endocrine Abstracts

P180