Giant cell tumour is a locally aggressive primary tumour, occurring mostly at the epiphysis of long bones. Although classified as benign, it can recur locally upto 50% cases and in 1-3% it cause spontaneous transformation to high grade malignancy. Surgical procedure (intra leisonal curettage with or without adjuvant therapy or en-bloc excision) is the mainstay of treatment. Systemic therapy includes Denosumab (RANKL inhibitor- Receptor activator of nuclear factor kappa-B ligand) and Zoledronic

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... cid (biphosphates). Zoledronic acid is a bisphosphonate given intravenously for the treatment of skeletal fractures in osteoporosis, Paget's disease, cancers such as multiple myeloma, prostate cancer and hypercalcaemia associated with malignancy. As per FDA (Food and drug administration) reports, Zoledronic acid causing myopathy is 0.3%. The possible common side effects of Zoledronic acid includes bone pain, nausea, fever, fatigue, anaemia, arthralgia, dizziness, insomnia and headache. In this report, we present a 12 year old boy who developed weakness on all 4 limbs and generalised body pain after receiving the first dose of Zoledronic acid. On investigating, he was diagnosed to have quadriparesis and his muscle functions (muscle power and plantar flexion) were decreased with preserved deep tendon reflexes. Initially, it was suspected as electrolyte abnormality induced myopathy. On laboratory investigation his electrolyte levels were normal, Vitamin D25 levels were low, creatinine kinase levels were high whereas calcium and phosphate levels were normal. These findings suggest the reaction has occurred due to Zoledronic acid and was managed with calcium and vitamin D3 supplements.