A 10-year-old boy is brought to the emergency department following an episode of generalized tonic-clonic seizure. Intravenous benzodiazepine was administered, terminating the patient's seizure. He has had no trauma, fever, headache, vomiting, or cough. For the last 2-3 months, the patient has had muscle pain and cramping that is exacerbated by exercise and relieved after a short rest. His mother states that for the past year his school performance has been deteriorating. Physical examination shows a sedated child who is arousable to painful stimuli. There are no dysmorphic features. Eye examination reveals pupils that are 3 mm in diameter and briskly reactive to light; bilateral cataracts are seen. The heart, lungs, and abdomen are normal. The patient moves all extremities on painful stimulation. Deep tendon reflexes are 3+ throughout. Serum calcium is 6 mg/dL, serum albumin is 3.8 g/dL, serum phosphorus is 8.2 mg/dL, and parathyroid hormone level is 150 pg/mL (normal: 10-65). A non-contrast CT scan of the head reveals calcification of the basal ganglia. Which of the following is the most likely cause of this patient's hypocalcemia?

Question

A 10-year-old boy is brought to the emergency department following an episode of generalized tonic-clonic seizure.  Intravenous benzodiazepine was administered, terminating the patient's seizure.  He has had no trauma, fever, headache, vomiting, or cough.  For the last 2-3 months, the patient has had muscle pain and cramping that is exacerbated by exercise and relieved after a short rest.  His mother states that for the past year his school performance has been deteriorating.  Physical examination shows a sedated child who is arousable to painful stimuli.  There are no dysmorphic features.  Eye examination reveals pupils that are 3 mm in diameter and briskly reactive to light; bilateral cataracts are seen.  The heart, lungs, and abdomen are normal.  The patient moves all extremities on painful stimulation.  Deep tendon reflexes are 3+ throughout.  Serum calcium is 6 mg/dL, serum albumin is 3.8 g/dL, serum phosphorus is 8.2 mg/dL, and parathyroid hormone level is 150 pg/mL (normal: 10-65).  A non-contrast CT scan of the head reveals calcification of the basal ganglia.  Which of the following is the most likely cause of this patient's hypocalcemia?

Quizplus · Accepted Answer

Explanation: 11ec2b69_c13a_a8bc_8f63_edc3c2d1aa28_MD0005_00 This patient has bilateral cataracts and basal ganglia calcifications consistent with chronic hypocalcemia. In combination with hyperphosphatemia and elevated parathyroid hormone (PTH), pseudohypoparathyroidism is the most likely diagnosis. PTH maintains calcium homeostasis by triggering calcium reabsorption and phosphate excretion in the kidneys. PTH also promotes calcium release from bone and increases active vitamin D to stimulate intestinal absorption of calcium. Pseudohypoparathyroidism is characterized by end-organ resistance to PTH; this results in chronic hypocalcemia, which signals increased PTH secretion through a biofeedback loop. Elevated PTH distinguishes pseudohypoparathyroidism from true hypoparathyroidism, which also causes hypocalcemia and hyperphosphatemia but is due to impaired PTH production (Choice B). calcium release from bone Hypocalcemia causes neuromuscular excitability (tetany), which can manifest as seizures, muscle cramping, paresthesias, hyperreflexia, or laryngospasm. Other findings of hypocalcemia include cardiotoxicity (eg, heart failure, QT prolongation) and psychosis (eg, anxiety, depression). Dysmorphic features (eg, short stature, round facies, short 4th/5th metacarpals) are present in a subtype of pseudohypoparathyroidism known as Albright hereditary osteodystrophy; however, these findings are absent in other subtypes. Laboratory evaluation is diagnostic, and treatment is calcium and vitamin D supplementation. (Choice A) Hyperphosphatemia can cause acutely decreased calcium levels typically due to seizure, tumor lysis, or acute renal failure. However, basal ganglia calcifications and cataracts occur only with chronic electrolyte derangements, so it is unlikely that hyperphosphatemia is contributing significantly to this patient's hypocalcemia. (Choice C) Primary hyperparathyroidism causes elevated PTH but increased calcium and decreased phosphorus levels. (Choice E) Vitamin D deficiency is characterized by a decrease in both calcium and phosphorus levels, along with increased PTH levels. In contrast, this patient's phosphorus level is elevated. Educational objective: Pseudohypoparathyroidism, caused by end-organ resistance to parathyroid hormone (PTH), causes chronic hypocalcemia, hyperphosphatemia, and elevated PTH. Seizures, muscle cramping, hyperreflexia, basal ganglia calcifications, and cataracts are signs of hypocalcemia. References: Pseudohypoparathyroidism with basal ganglia calcification: a case report of rare cause of reversible parkinsonism. (http://www.ncbi.nlm.nih.gov/pubmed/28296742) Pseudohypoparathyroidism - epidemiology, mortality and risk of complications. (http://www.ncbi.nlm.nih.gov/pubmed/26387561)

A 10-Year-Old Boy Is Brought to the Emergency Department Following