On an interesting note, supplementing patients' diet with tryptophan improved sleep, but worsened the musculoskeletal pain. Substance P fails to dampen the discharge of sensory nerves with a serotonin deficiency. The cytolytic activity of natural killer cells is significantly lower when serotonin is decreased. Glycolysis impairment prevents activation of thiamine leading to serotonin deficiency and energy depletion. Increased prostaglandin E2 sensitizes peripheral nerve endings and lowers their threshold of pain when substance P is present.
Endorphins have less ability to reduce pain when serotonin is low.
Catecholamine levels rise during stress responses and have been found elevated in the urine of FM patients. No correlation has been found between the clinical features of FM and the psychologic status of the patient. Fibromyalgia does not appear to be depression, anxiety, or stress, although all of these contribute to enhanced pain. Fibromyalgia, chronic fatigue, irritable bowel syndrome, and depression may share a common physiologic abnormality. Some doctors believe repressed guilt may play a role in this syndrome also.