Profound Hypocalcemia Following Thyroidectomy for Graves’ Disease

Abstract

\n Introduction: While transient parathyroid insufficiency is not an uncommon complication of thyroidectomy, severe and prolonged hypocalcemia attributed to a combination of post-surgical hypoparathyroidism, hungry bone syndrome (HBS) and hypovitaminosis D is unusual.\n Clinical Case: A 17-year-old female from a remote community in Australia with Graves’ disease, complicated by exophthalmos and atrial flutter, underwent total thyroidectomy due to challenges with medication adherence leading to persistent thyrotoxicosis. FT4 was >150 pmol/L (normal 10–20 pmol/L) almost two years after diagnosis. Pre-operatively, she received Lugol’s iodine, carbimazole and beta-blockade. The operation was uncomplicated and three parathyroid glands were preserved. Within six hours of thyroidectomy, she developed symptomatic hypocalcemia with corrected calcium 1.9 mmol/L (7.6 mg/dL) (normal 2.2–2.65 mmol/L). PTH level was 0.8 pmol/L (normal 1.4–9.0 pmol/L). Magnesium and phosphate levels were initially normal but hyperphosphatemia developed the following day. 25-OH vitamin D was low (29 nmol/L, normal 50–150 nmol/L) and was corrected with high dose cholecalciferol.\n Despite use of continuous intravenous calcium gluconate in addition to oral calcium carbonate, as well as both intravenous and oral calcitriol and magnesium, urinary calcium excretion remained undetectable. Teriparatide 20 mcg BD was commenced on post-operative day 14 with no demonstrable improvement in serum calcium. Less than 48 hours after cessation of parenteral calcium on day 18 post-operation, corrected calcium and ionised calcium declined to 1.47 mmol/L (5.9 mg/dL) and 0.46 mmol/L (normal 1.15–1.33 mmol/L) respectively, prompting recommencement of calcium infusion.\n Her remarkably high requirement for calcium replacement with negligible urinary calcium excretion for at least one month in spite of parenteral calcium infusion for a total of three weeks’ duration is highly suggestive of HBS which became evident due to post-surgical hypoparathyroidism. She had elevated ALP (618 U/L, normal 35–140 U/L) and increased bone resorption marker (N-telopeptide/creatinine 262 nmol BCE/mmol, normal <100 nmol BCE/mmol), with osteopenia at lumbar spine (Z-score -1.7) and femur (Z-score -1.3). Additionally, vitamin D deficiency is likely to have contributed to the severity of hypocalcemia.\n 60 days after surgery, she was still requiring calcium carbonate 2500 mg QID (4 g/day elemental calcium) and calcitriol 1 mcg TDS. Her phosphate level had normalised and ALP gradually declined to 241 U/L.\n Clinical Lesson: This case highlights the importance of attaining euthyroid status as early as possible pre-operatively to allow near-complete reversal of thyrotoxicosis-induced osteodystrophy, as indicated by normalisation of serum ALP, and ensuring vitamin D levels are replete prior to thyroidectomy for Graves’ disease.