Differential Diagnosis
- Single most likely diagnosis + E) Increased serum thyroid-stimulating immunoglobulin concentration: This is the most likely cause of the patient's condition, given her symptoms of hyperthyroidism, such as tachycardia, weight loss despite increased appetite, frequent bowel movements, difficulty sleeping, and heat intolerance. The presence of a firm and enlarged thyroid gland, lid lag, and brisk deep tendon reflexes further support this diagnosis. The family history of acquired hypothyroidism treated with thyroid hormone replacement therapy may also suggest an autoimmune component, which is consistent with Graves' disease, the most common cause of hyperthyroidism in children.
- Other Likely diagnoses + D) Increased serum metanephrine concentration: Although less likely, an increased serum metanephrine concentration could explain some of the patient's symptoms, such as tachycardia, hypertension, and difficulty sleeping, which are also seen in pheochromocytoma. However, the presence of a goiter and other symptoms more typical of hyperthyroidism make this diagnosis less likely.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.) + A) Atrial fibrillation: Although atrial fibrillation is not a primary diagnosis that explains all the patient's symptoms, it is a potential complication of untreated hyperthyroidism. Missing this diagnosis could lead to severe consequences, including stroke or heart failure. + B) Atrioventricular re-entrant tachycardia: Similar to atrial fibrillation, atrioventricular re-entrant tachycardia is a potential cardiac complication that could arise in the context of hyperthyroidism, especially if left untreated. It is crucial to consider and rule out such arrhythmias to prevent adverse outcomes.
- Rare diagnoses + C) Increased plasma renin activity: This would be more indicative of renovascular hypertension or other conditions affecting the renin-angiotensin-aldosterone system. While it could explain hypertension, it does not account for the majority of the patient's symptoms, making it a less likely and rare consideration in this context.