Missy Elliot’s weight loss, seen at last year’s VH-1 Hip Hop Honors Awards, could possibly be credited to something more than just diet and exercise. On Thursday the rapper revealed that she's been suffering from Graves' disease for the past three years.

What is Graves' disease?

According to the National center for Biotechnology Information, Graves' disease is an auto-immune disorder that leads to overactivity of the thyroid gland. The thyroid gland controls metabolism and is critical for regulating mood, weight, mental and physical energy levels. Graves' disease is most common in women over age 20. However, the disorder may occur at any age and may affect men as well.

Elliot explained how everyday tasks are difficult for her. “I couldn’t write because my nervous system was so bad—I couldn’t even use a pen,” she told People.

How can it be treated?

Beta-blockers such as propranolol are often used to treat symptoms of rapid heart rate, sweating and anxiety until the hyperthyroidism is controlled.

The disease can also be treated by anti-thyroid medications, radioactive iodine or surgery. Elliot has undergone radiation therapy and spent time at the gym to help her get better.

If diagnosed properly, a person can live a relatively normal life.

Elliot refuses to let the disease to keep her down. Her seventh studio album is expected to be released this year.

What are the symptoms?

Elliot suffered hair loss, mood swings and lack of muscle control. Other symptoms include:

—Anxiety

—Breast enlargement in men (possible)

—Difficulty concentrating

—Double vision

—Eyeballs that stick out (exophthalmos)

—Eye irritation and tearing

—Fatigue

—Frequent bowel movements

—Goiter (possible)

—Heat intolerance

—Increased appetite

—Increased sweating

—Insomnia

—Menstrual irregularities in women

—Muscle weakness

—Nervousness

—Rapid or irregular heartbeat (palpitations or arrhythmia)

—Restlessness and difficulty sleeping

—Shortness of breath with exertion

—Tremor

—Weight loss (rarely, weight gain)

(Photo: Don Arnold/Getty Images)