Thyrotoxicosis refers to the biochemical and physiological manifestations of excessive thyroid hormone.
Hyperthyroidism is a term reserved for disorders that result in the over production of hormone by the thyroid gland. Thyrotoxicosis need not be due to hyperthyroidism.
Causes of hyperthyroidism
Jod - Basedow's disease
Toxic nodular goiter
Causes of thyrotoxicosis without hyperthyroidism
Ectopic functioning thyroid tissue
Metastatic follicular carcinoma