Rare paraneoplastic syndrome, related in the majority of cases to a mesenchymatous tumor (variable size and topography)  that inappropriately secretes a phosphorus lowering substance (phosphatonine), usually FGF-23 (fibroblast growth factor 23). FGF-23 inhibits the renal tubular reabsorption of phosphorus at the level of the proximal tubule by blocking the sodium/phosphorus co-transporters that are dependent of the MAPKinases . It also lowers the hydroxylation of vitamin D by stopping the synthesis of 1-alpha-hydroxylase.

Clinical presentation: severe, rapidly progressive, extremely painful osteomalacia associated with signs of myopathy (early muscle deficit of proximal topography). Bone pain is very intense, and correspond to multiple lesions (fractures or pseudofractures) scattered throughout the skeleton. Imaging confirms the presence of demineralization associated with pseudofractures, of the Looser-Milkman type. Biologically, hypophosphatemia with elevated level of alkaline phosphatases, without calcium , 25 (OH) D3 nor  parathormone anomalies. But phosphaturia is high, sign of a phosphorus diabetes (Cl P > 20 ml/min).

Anesthetic implications:

bone fragility; monitoring of curarization (myopathy); hypophosphatemia can cause respiratory weakness by hypocontractility of the diaphragm and cardiac complications (rhythm disorders, heart failure) (ECG and echocardiogram), as well as a reduction of the response to insulin (blood sugar).

References:

-         Poizat F, Wojtusciszin A, Raynaud P, Maître H, Renard E, Baldet P.
Tumeur du pied et douleurs diffuses : un cas d’ostéomalacie oncogénique.
Ann Pathol 2005 ; 25 : 134-7.

-        Bosse C, Fournel L, Canny-Hamelin E.
Tumeur mésenchymateuse thoracique: une cause rare d’ostéomalacie.
Chir Thor Cardiovasc 2016 ; 20 :55-7.

-        Verma A, Tewari S, Kannaujia A.
Perioperative management of patients with severe hypophophataemia secondary to  oncogenic osteomalacia: our experience and review of the literature.
Indian J Anaesth 2017; 61: 590-3.

Updated September 2017*