Endocrine Abstracts

Background

Secondary hyperparathyroidism is a condition that can occur as a result of low vitamin D level. Parathyroid hormone (PTH) has the role of stimulating bone resorption by two mechanisms: direct activation of osteoblasts and indirect stimulation of osteoclast. Exostosis or bone spur is a benign tumor that consists in overgrowth of a pre-existing bone. Exostoses can affect any bone, however they are most commonly located on the bones of the joints such as: the ribs, hips, knees, ankles, shoulders and elbows. Their exact cause is not known, however, they appear mostly during the active growth stages and as a result of bone lesion. They can cause chronic pain or can be asymptomatic and discovered incidentally.

Case presentation

We herein report the case of a 10-year-old Caucasian girl who presented to the orthopaedic ward complaining of leg pain during walking. The radiologic investigation showed a lateral exostosis above the right knee. The patient’s family physician referred her to our endocrinology clinic. Her pubertal stage was Tanner IV for breast growth and Tanner IV for pubic hair development. Biochemical investigations showed elevated PTH level 91.4 pg/ml (normal range, 15–68 pg/ml), low vitamin D level 23.5 ng/dl (normal range, >30 ng/ml), normal calcemia, urinary calcium/creatinine ratio <0.2 mg/dl (normal range, <0.14 mg/dl) and normal thyroid hormone levels. The diagnosis established was secondary hyperparathyroidism due to vitamin D insufficiency. The patient received replacement therapy with cholecalciferol (2000 IU) under which the levels of PTH turned within normal range.

Conclusion

This case illustrates the unusual association of exostosis located above the knee in a patient with secondary hyperparathyroidism caused by low vitamin D level. Although there is only the possibility of a casual association, this case is noteworthy to report because of its interesting features. We highlight the importance of vitamin D replacement in childhood, for it can prevent secondary hyperthyroidism along with its consequences.