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Hyperthyroidism in multinodular goitre |
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Functional autonomy with thyroid hormone synthesis and secretion even in the absence of TSH is a characteristic feature of multinodular goitre. Hyperfunctioning areas may develop as nodules or be scattered in internodular tissue (fig. 4).
Autonomous thyroid hormone secretion tends to increase gradually over years with a concommittant decrease in pituitary TSH secretion. This keeps the patient euthyroid. The balance can be disturbed by a sudden iodine load to the patient leading to transient hyperthyroidism (fig. 5).
Figure 5:
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Various types of progression of autonomous hormone secretion in multinodular goitre. Note the difference in speed of progression and the transient increase induced by high iodine intake in patient 3. When autonomous hormone secretion exceeds physiological hormone secretion the patient becomes hyperthyroid. |
Even without an iodine load the disease tends to proceed, with a course varying widely between patients. Different patterns of disease progression towards hyperthyroidism are illustrated in fig. 5.
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