Increased levothyroxine requirements presenting as "inappropriate" TSH secretion syndrome in a patient with nephrotic syndrome

Exacerbation of underlying hypothyroidism caused by proteinuria and induction of urinary thyroxine loss: case report and subsequent investigation

OBJECTIVE

To describe a patient with excess urinary thyroxine (T4) excretion and worsening of preexisting hypothyroidism in the setting of nephrotic syndrome and to determine whether excess urinary T4 excretion is present in other patients with proteinuria.

METHODS

We present data regarding the patient's initial presentation, diagnostic studies, and course of her illness. We suspected urinary T4 loss to be the cause of her presentation and analyzed her urine sample for total T4. We also analyzed differences in urinary T4 excretion in 22 patients with proteinuria and 16 control patients without proteinuria. Relevant medical literature is reviewed.

RESULTS

A 44-year-old woman presented with a 3-month history of increasing fluid retention, weight gain, and fatigue. She had long-standing hypothyroidism on a stable levothyroxine dosage, 125 mcg/d. She had gained 27 kg and had developed significant edema. She had a grossly elevated thyroid-stimulating hormone level of 91 mIU/L. Her condition worsened, and a urinary protein measurement was 14.06 g/24 h-diagnostic of nephrotic syndrome. The levothyroxine dosage was increased to 225 mcg/d. Urinary total T4 concentration in a 24-hour sample was 59.0 microg/L (83.1 microg/24 h), indicating that a substantial fraction of her orally ingested T4 was lost in urine. Urinary total T4 excretion was significantly higher in patients with proteinuria (mean +/- standard deviation, 18.0 +/- 18.2 microg/L) vs control patients without proteinuria (mean, 3.8 +/- 1.8 microg/L) (P = .0014).

CONCLUSION

In the patient described, urinary T4 loss due to proteinuria and nephrotic syndrome resulted in a severe exacerbation of underlying hypothyroidism.

Hypothyroidism

Hypothyroidism is common, potentially serious, often clinically overlooked, readily diagnosed by laboratory testing, and eminently treatable. The condition is particularly prevalent in older women, in whom autoimmune thyroiditis is common. Other important causes include congenital thyroid disorders, previous thyroid surgery and irradiation, drugs such as lithium carbonate and amiodarone, and pituitary and hypothalamic disorders. Worldwide, dietary iodine deficiency remains an important cause. Hypothyroidism can present with nonspecific constitutional and neuropsychiatric complaints, or with hypercholesterolaemia, hyponatraemia, hyperprolactinaemia, or hyperhomocysteinaemia. Severe untreated hypothyroidism can lead to heart failure, psychosis, and coma. Although these manifestations are neither specific nor sensitive, the diagnosis is confirmed or excluded by measurements of serum thyrotropin and free thyroxine. Thyroxine replacement therapy is highly effective and safe, but suboptimal dosing is common in clinical practice. Patient noncompliance, drug interactions, and pregnancy can lead to inadequate treatment. Iatrogenic thyrotoxicosis can cause symptoms, and, even when mild, provoke atrial fibrillation and osteoporosis. We summarise present understanding of the history, epidemiology, pathophysiology, and clinical diagnosis and management of hypothyroidism.

Renal metastases from thyroid papillary carcinoma: study of sodium iodide symporter expression

Kidney metastases from thyroid cancer are rare. We report two such patients and demonstrate that the in vivo 131I uptake by the kidney metastasis is associated with high levels of sodium iodide (Na+/I-) symporter (NIS) expression in the first case. Case 1: A 61-year-old woman with papillary thyroid carcinoma-follicular variant (PTC-FV) presented with scapular metastasis. After thyroidectomy and scapulectomy, a 131I posttherapy scan showed left upper quadrant uptake. A 3.0-cm metastatic PTC-FV deposit was removed by partial nephrectomy. Case 2: A 53-year-old woman presented with back pain. A computed tomography (CT) scan showed a 3.5-cm renal mass, a multinodular goiter, and lung metastases thought secondary to a renal cell carcinoma. A unilateral nephrectomy revealed metastatic PTC-FV. After thyroidectomy, a 131I posttherapy scan showed lung and skeletal metastases. NIS immunoreactivity in tumoral tissue was strongly positive in the primary tumor, shoulder, and kidney metastasis in case 1, as well as in the primary tumor in case 2. Spotty, low-level NIS expression was observed in the kidney metastasis in case 2. In conclusion, kidney metastases of PTC-FV may occasionally retain adequate levels of NIS expression, enabling their detection during life. Thus, intense uptake in the abdomen during 131I imaging should not be assumed to be physiological gastrointestinal tract residual radionuclide activity.