Glossary
Pituitary pars intermedia dysfunction (PPID).
Direct answer
Pituitary pars intermedia dysfunction is an age-associated disorder in which the braking control exerted by the brain over one specific part of the pituitary gland weakens. That part enlarges and releases more hormone. Usual signs include a long coat that sheds late, loss of muscle and an increased tendency to laminitis.
The old label equine Cushing's disease is misleading. In people, Cushing's disease arises in the anterior lobe of the pituitary and revolves around cortisol. In the horse the change involves the intermediate lobe, whose cells are normally restrained by dopamine: the mechanism differs, and a markedly raised cortisol is not part of the picture.
Season is decisive for laboratory testing. In healthy horses, hormone values rise physiologically in late summer and autumn, so reference intervals have to be season-specific. A single value quoted without its date is hard to interpret. In addition, equine metabolic syndrome shares some features and may be present at the same time.
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