An 80‑year‑old woman not taking any thyroid medication has a suppressed thyroid‑stimulating hormone, elevated free thyroxine and low‑normal free triiodothyronine; what is the most likely cause and how should it be evaluated and managed?

Evaluation and Management of Suppressed TSH with Elevated Free T4 and Low-Normal Free T3 in an 80-Year-Old Woman Not on Thyroid Medication

The most likely cause is endogenous subclinical hyperthyroidism due to toxic multinodular goiter or a solitary toxic adenoma, and this patient requires immediate evaluation with a thyroid ultrasound, radioactive iodine uptake scan, and assessment for cardiovascular complications—particularly atrial fibrillation—given the substantial morbidity and mortality risks in elderly patients with suppressed TSH.

Most Likely Diagnosis

This biochemical pattern—suppressed TSH, elevated free T4, and low-normal free T3—in an 80-year-old woman not taking thyroid medication is diagnostic of endogenous subclinical or overt hyperthyroidism. 1, 2

• The suppressed TSH with elevated free T4 definitively excludes primary hypothyroidism, central hypothyroidism, and non-thyroidal illness 1, 2
• In elderly patients with this pattern, the most common causes are toxic multinodular goiter or solitary toxic adenoma, rather than Graves' disease 3, 2
• The low-normal free T3 is typical in elderly hyperthyroid patients and does not exclude the diagnosis—this represents "T4 toxicosis" where T4 is elevated but T3 conversion is impaired by age 1, 2
• Thyroid autoantibodies (anti-TPO, anti-thyroglobulin, TSH receptor antibodies) are uncommon in elderly patients with toxic nodular disease, unlike younger patients with Graves' disease 2

Critical Immediate Evaluation

Cardiovascular Assessment (Highest Priority)

The most urgent priority is screening for atrial fibrillation and other cardiac complications, as elderly patients with suppressed TSH have a 3-5 fold increased risk of atrial fibrillation and substantially elevated cardiovascular mortality. 4, 3

• Obtain an electrocardiogram immediately to screen for atrial fibrillation, as this is the most serious acute complication 4, 3
• Assess for signs of heart failure, including dyspnea, peripheral edema, and elevated jugular venous pressure 4
• Measure blood pressure, as hyperthyroidism can cause systolic hypertension 4
• If atrial fibrillation is detected, anticoagulation and rate control become immediate priorities 4, 3

Thyroid Imaging and Functional Studies

Obtain a thyroid ultrasound and radioactive iodine uptake scan with imaging to differentiate toxic multinodular goiter from solitary toxic adenoma versus Graves' disease. 1, 2

• Thyroid ultrasound will identify nodular disease, which is the most common cause in elderly patients 2
• Radioactive iodine uptake and scan will demonstrate areas of autonomous function (hot nodules) in toxic adenoma or multinodular goiter 1, 5
• In Graves' disease, the uptake would be diffusely elevated, but this is less common in the elderly 2
• Measure thyroid autoantibodies (TSH receptor antibodies, anti-TPO, anti-thyroglobulin) to assess for Graves' disease, though these are typically negative in toxic nodular disease 2

Bone Health Assessment

Assess for osteoporosis risk, as prolonged TSH suppression causes significant bone mineral density loss and increases fracture risk, particularly in postmenopausal women. 4, 3

• Consider bone density assessment (DXA scan) given the patient's age and sex 4
• Ensure adequate calcium (1200 mg/day) and vitamin D (1000 units/day) intake 4
• Screen for history of fractures, particularly hip and spine fractures 4

Confirmatory Laboratory Testing

Repeat TSH, free T4, and add free T3 measurement after 3-6 weeks to confirm persistent suppression and rule out transient causes. 1, 2

• A single abnormal TSH can be transient due to acute illness, medications, or assay interference 4, 6
• Measure free T3 by equilibrium dialysis if available, as some patients have isolated T3 toxicosis despite normal total T3 1
• If free T3 is elevated on repeat testing, this confirms overt hyperthyroidism requiring treatment 1
• If free T3 remains normal but TSH remains suppressed with elevated free T4, this represents subclinical hyperthyroidism with T4 predominance 1, 2

Management Algorithm

If Overt Hyperthyroidism (Elevated Free T3 or Symptomatic)

Initiate treatment with radioactive iodine ablation or antithyroid drugs, as untreated hyperthyroidism in the elderly carries unacceptable cardiovascular and bone risks. 3, 1

• Radioactive iodine is the preferred definitive treatment for toxic nodular disease in elderly patients 1
• Beta-blockers (e.g., metoprolol 25-50 mg twice daily) should be started immediately for symptom control and to reduce atrial fibrillation risk 3
• Antithyroid drugs (methimazole 5-10 mg daily) can be used as a bridge to radioactive iodine or in patients who refuse definitive therapy 3

If Subclinical Hyperthyroidism (Normal Free T3, Suppressed TSH, Elevated Free T4)

Treatment is strongly recommended in patients over 60 years with TSH <0.1 mIU/L due to high risk of atrial fibrillation, osteoporosis, and cardiovascular mortality. 4, 7, 3

• For TSH <0.1 mIU/L with cardiac disease, atrial fibrillation, or osteoporosis risk, treatment is mandatory 4, 7
• For TSH 0.1-0.4 mIU/L, monitor every 3-12 months and treat if symptomatic or high-risk features develop 4, 7
• Approximately 1% per year of elderly patients with TSH 0.1-0.4 mIU/L progress to overt hyperthyroidism 7
• Spontaneous TSH normalization occurs in approximately 24% of cases over 3-4 years, but this cannot be predicted 7, 2

Special Considerations in the Elderly

Elderly patients with hyperthyroidism often present with atypical symptoms—apathy, weight loss, and cognitive decline—rather than classic hypermetabolic symptoms. 3, 2

• The Wayne clinical index score is often lower in elderly hyperthyroid patients compared to younger patients 2
• Fatigue and weakness may predominate over heat intolerance and tremor 3, 2
• Cognitive impairment and dementia are associated with subclinical hyperthyroidism in the elderly 4
• Weight loss without increased appetite is common 3

Critical Pitfalls to Avoid

• Never assume a suppressed TSH with elevated free T4 is due to non-thyroidal illness in an outpatient setting—this pattern indicates true hyperthyroidism requiring evaluation 1, 2
• Do not delay cardiovascular assessment—atrial fibrillation can develop acutely and requires immediate management 4, 3
• Avoid assuming the patient is asymptomatic based on absence of classic hyperthyroid symptoms—elderly patients have atypical presentations 3, 2
• Never ignore low-normal free T3 as excluding hyperthyroidism—T4 toxicosis with impaired T3 conversion is common in the elderly 1, 2
• Do not wait for symptoms to worsen before treating—cardiovascular and bone complications occur silently 4, 3

Monitoring Strategy

If treatment is initiated, recheck TSH, free T4, and free T3 at 6-8 weeks after radioactive iodine or dose adjustment of antithyroid drugs. 4

• Target TSH should be 0.5-4.5 mIU/L with normal free T4 and free T3 4
• After radioactive iodine, many patients develop hypothyroidism requiring levothyroxine replacement 4
• Monitor for atrial fibrillation recurrence even after TSH normalization 4, 3
• Continue bone health monitoring with DXA scans every 1-2 years if osteoporosis is present 4