The parathyroid glands are small glands, located at the back of the thyroid gland in the front of the neck. They produce parathyroid hormone (PTH) which is vital in controlling calcium levels in the blood. Even small changes in calcium levels can have catastrophic effects. Although these glands are only the size of rice grains normally, one or more of them may increase in size and become hyperactive, producing more PTH than the body needs. This leads to a rise in the blood calcium, which may cause thinning of the bones (osteoporosis), kidney damage or kidney stones.
What is vastly underestimated, in my opinion, are the psychological and mood symptoms caused by this dysfunction. Tiredness, irritability, mood swings, depression, forgetfulness and the feeling of a fog in the mind are all well-described symptoms. Of course, these are very non-specific and there is no simple test that will quantify these symptoms.
Diagnosing parathyroid disease takes skill and often blood tests and sophisticated imaging. However, once the diagnosis is made, it can often be cured with surgery (parathyroidectomy), not simply managed or kept at bay.