P075 What has parenteral iron got to do with rheumatology?
Authors: Achilleos Katerina M , Rajagopal Vivek , Adams Claire , Clunie Gavin 
Published: April 2024

Abstract

Background/Aims
A 39 year-old female had been experiencing a six-month history of insidious onset migratory joint and bone pain, stiffness, malaise and over the last four months proximal muscle weakness. There had been partial relief with the use of non-steroidal anti-inflammatory medication. Past medical history included severe menorrhagia secondary to fibroids with a haemoglobin of 50g/dl on a handful of occasions, requiring x3 iron infusions (Ferric Carboxymaltose (FCM)1000mg) over a two year period. The last two infusions were provided three months apart. After each infusion, profound fatigue ensued. A blood test demonstrated an elevated ALP 301 (RR 30-130 U/L), reduced phosphate 0.48 (RR 0.8-1.5mmol/L) and mildly reduced 25OH vitamin D 44 (RR 50-140nmol/L). Corrected calcium was low-normal 2.29 (RR 2.2-2.6mmol/L) as was PTH 4.62 (RR 1.6-6.9pmol/L). A CTCAP excluded malignancy.

Methods
The patient had been treated with Cholecalciferol 1000iu and Dipyridamole 100mg daily with weekly blood test monitoring for six weeks prior to review in the metabolic bone clinic. Dipyridamole aided biochemical and symptomatic improvement. Further tests returned with an elevated FGF23 252 (RR 0-100 RU/ml), a normal Urine phosphate/Creatinine 1.6 and TmP/GFR ratio (suggesting the FGF23 effect on the kidney was not severe or its effects inhibited by Dipyridamole). ALP had reduced slightly to 269, PTH was elevated at 10.81 (RR 1.95-8.49micromol/L) and 1,25 Dihydroxy Vit D 182 (RR43-144 pmol/L).

Results
The patient was diagnosed with Parenteral iron triggered hypophosphatemia osteomalacia (6H-syndrome). A delayed diagnosis and referral resulted from unfamiliarity of side-effects of parenteral iron, especially Ferric Carboxymaltose, which has an alert on the GOV.UK website. The patient discontinued IV iron and was placed on oral Ferrous Gluconate 300mg daily. In retrospect, bone and joint pain was likely the result of enthesial pain and pseudofractures. In patients with diagnostic uncertainty, an isotope bone scan would be beneficial in assessing the extent of such pseudofractures. Hypophosphatemia is common following FCM (≥1/100 to &lt; 1/10), and often self-limiting and asymptomatic. However, sustained hypophosphatemia (from recurrent infusions) can result in osteomalacia. Both anaemia and certain iron preparations can cause an elevation in FGF23 leading to increased urinary phosphate excretion. Dipyridamole has anti-phosphaturic effects by inhibiting FGF23.

Conclusion
It is advised in such patients to monitor serum phosphate levels at two- and five-weeks post infusion and to re-evaluate therapy with FCM in patients with persistent hypophosphatemia. It is common for symptoms, imaging, and biochemistry (FGF23 and ALP) to remain elevated/positive several months after diagnosis. This case highlights the need to ask about iron infusions in the drug history in patients presenting with hypophosphatemia and to be aware that musculoskeletal pain following iron infusions can be a sign of osteomalacia which will need investigating. Rarely, proximal muscle weakness can occur following the above iron preparation.

Disclosure
K.M. Achilleos: None. V. Rajagopal: None. C. Adams: None. G. Clunie: None.