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Researchers found that abnormal structural changes in areas of the brain involved in pain and emotion can be seen on MRI in young women with primary dysmenorrhea, and persist even when the women are not experiencing cyclic menstrual pain.

When MRI scans were performed during the pain-free peri-ovulatory period of the menstrual cycle, changes were observed in regions of the brain involved in pain transmission and higher sensory processing, as well as in regions involved in endocrine function and pain modulation, explained Dr. Cheng-Hao Tu of the National Yang-Ming University in Taipei and colleagues.

Studies of patients with chronic pain have shown that extended pain messages delivered to the central nervous system can lead to structural and functional alterations throughout the nervous system, the researchers wrote online in Pain.

But such changes had not been elucidated for cyclic pain, such as is seen in menstrual cramping, so Tu and colleagues enrolled 32 women with severe menstrual pain and 32 control subjects who did not experience this disorder.

No significant differences were seen on MRI for total volume of the tisuses in the brain known as gray matter between patients and controls, but numerous regional differences in gray matter were detected.

One area of the brain in which changes in volume were seen was an area known as the hypothalamus. This area was of particular interest because of its central role in regulating the menstrual cycle.

The study results should be interpreted with caution, the authors stated, because with current MRI techniques the contribution of other factors such as changes in spine/synapse density and blood flow cannot be measured.

"Our results demonstrated that abnormal [gray matter] changes were present in [primary dysmenorrhea] patients even in the absence of pain. This shows that not only sustained pain but also cyclic occurring menstrual pain can result in longer lasting central changes," the researchers concluded.

The functional consequences of these findings remain to be analyzed, and longitudinal studies are needed to explore hormonal interactions and whether the brain changes are reversible.

Source: BBC News