Table 2 Differential diagnosis of thyrotoxicosis

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RAIU Elevated

RAIU Reduced

Common Graves' disease

Toxic multinodular goitre Toxic adenoma

Subacute thyroiditis Silent thyroiditis

Uncommon TSH-secreting pituitary adenoma Thyroid hormone resistance

(partial) Trophoblastic tumors

Exogenous thyroxine

(factitious) Iodine-induced (JodBasedow effect) Struma ovarii syndrome Thyroid cancer metastases

Graves' disease may appear at any age but occurs most often in females aged 2050 years. The presenting signs and symptoms are secondary to: an increased metabolic rate, increased adrenergic activity and manifestations of infiltrative dermopathy and ophthalmopathy. Patients may present with complaints of heat intolerance, weight loss in spite of an increased appetite, loose stools, tachycardia, tremor, emotional lability, fatigue and insomnia. Children may present with hyperactivity. In contrast, elderly patients may appear depressed and apathetic, having withdrawn from customary activities.

On examination, untreated patients may appear nervous and hyperactive or fatigued and listless. With Graves' disease, there is commonly mild to severe diffuse thyroid enlargement of the gland which has been described as having a "beefy" consistency. Bruits may be audible over the gland, the skin is warm and moist. There may be tremor of the outstretched hands and tachycardia is commonly observed. Thyrotoxic stare, lid retraction and lid lag may be present. Clinical signs of infiltrative ophthalmopathy are seen in fewer than one-half of patients on presentation. Pretibial myxedema and thyroid acropachy are relatively rare findings. Treatment with beta blocking drugs may abolish the signs of adrenergic overactivity (eg. tremor, tachycardia, stare and lid lag). The use of beta blockers does not compromise diagnostic testing with radionuclides.

In Figure 3 the 99mTc-pertechnetate thyroid scans of common thyroid disorders, including a typical patient with Graves' disease, are displayed. On occasion, patients with other forms of chronic thyroid disease may develop TSH receptor antibodies producing a thyrotoxic state. The distinction is not very important except that the latter may be at lower risk of developing eye complications. In these cases, the radionuclide pattern may be somewhat patchy rather than the diffuse homogenous pattern of uptake seen with Graves' disease.

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