Editing Cushing's syndrome (section)

=== Hyperpigmentation ===
Cushing's syndrome due to excess [[ACTH]] may also result in [[hyperpigmentation]]. This is due to [[melanocyte-stimulating hormone]] production as a byproduct of ACTH synthesis from pro-opiomelanocortin (POMC). Alternatively, it is proposed that the high levels of ACTH, [[β-lipotropin]], and [[lipotropin|γ-lipotropin]], which contain weak MSH function, can act on the [[melanocortin 1 receptor]]. A variant of Cushing's disease can be caused by ectopic, i.e. extra pituitary, ACTH production from, for example, a small-cell lung cancer.<ref name="auto">{{cite web |url=https://www.lecturio.com/concepts/cushings-syndrome/| title=Cushing's Syndrome
|website=The Lecturio Medical Concept Library |access-date= 11 July 2021}}</ref>

When Cushing's syndrome is caused by an increase of cortisol at the level of the adrenal glands (via an adenoma or hyperplasia), [[negative feedback]] ultimately reduces ACTH production in the pituitary. In these cases, ACTH levels remain low and no hyperpigmentation develops.<ref name="auto"/>