Hyperthyroidism
A state of thyroid hormone excess that accelerates metabolic rate across almost every tissue, so the clinical picture (weight loss despite hunger, heat intolerance, tachycardia and tremor) can be derived directly from asking what a sped-up metabolism looks like.
Definition
Hyperthyroidism is excess production of thyroid hormone by the thyroid gland, causing thyrotoxicosis (the clinical effects of high circulating thyroid hormone). Graves' disease is the commonest cause; others include toxic multinodular goitre and toxic adenoma.
First principles
Thyroid hormone excess is metabolism running too fast, mirroring hypothyroidism in reverse
Just as thyroid hormone deficiency slows basal metabolic rate, excess accelerates it: increased oxygen consumption, heat production and catabolism of fat, muscle and bone. Because this drive touches nearly every organ, the resulting symptoms span cardiovascular, neurological, gastrointestinal and dermatological systems simultaneously, a single mechanism expressed everywhere at once.
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