Differentials
Graves disease
SIGNS / SYMPTOMS
Exophthalmos or pretibial myxedema may be present.
Onset and symptoms often more dramatic than for toxic nodule.
INVESTIGATIONS
Thyroid scan shows diffuse uptake.
Thyroid-stimulating hormone (TSH) receptor antibodies are positive.
Toxic multinodular goiter
SIGNS / SYMPTOMS
Patients usually >40 to 50 years of age.
Apathetic hyperthyroidism more likely, with weight loss, mood change or atrial fibrillation alone.[29]
INVESTIGATIONS
Scan shows areas of both increased and decreased uptake, indicating nonfunctioning and functioning nodules.[1][Figure caption and citation for the preceding image starts]: Thyroid scan showing variegated uptake in toxic multinodular goiterCourtesy of Dr Elizabeth Pearce [Citation ends].
Uptake often normal.
Thyrotoxic phase of painless lymphocytic thyroiditis
SIGNS / SYMPTOMS
Most often occurs postpartum.
INVESTIGATIONS
Absent or low uptake on I-123 scan.
Often there is evidence of thyroid autoimmunity (i.e., positive thyroid peroxidase antibodies), although this is not diagnostic.
Thyrotoxic phase of subacute granulomatous thyroiditis
SIGNS / SYMPTOMS
Associated with anterior neck pain and tenderness.
INVESTIGATIONS
Absent or low uptake on I-123 scan.
Erythrocyte sedimentation rate (ESR) elevated.
Iodine-induced hyperthyroidism
SIGNS / SYMPTOMS
History of an iodine load (from iodinated radiographic contrast, amiodarone, or a change in diet) in the setting of autonomous nodular thyroid disease (the Jod-Basedow phenomenon).[1]
INVESTIGATIONS
Low uptake on I-123 scan.
24-hour urine iodine high.
Marine-Lenhart syndrome (nodular Graves disease)
SIGNS / SYMPTOMS
Exophthalmos or pretibial myxedema may be present.
INVESTIGATIONS
Thyroid scan shows diffuse uptake with a cold rather than hot area in the region of the palpable nodule. The nodule appears hot on scan only following treatment for Graves disease.[32]
Functional follicular thyroid cancer
SIGNS / SYMPTOMS
Very rare.
There may be bulky metastatic disease or cervical lymphadenopathy.
INVESTIGATIONS
Total body scan shows uptake of radioactive iodine over metastases.
Thyroidal hemiagenesis plus Graves disease
SIGNS / SYMPTOMS
Very rare.
Exophthalmos or pretibial myxedema may be present.
INVESTIGATIONS
Ultrasound shows absence of the contralateral lobe.[33]
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