Table 10 Summary of findings for objective markers

Genetics

Polymorphisms in catecholamine o-methyl transferase have been noted in some ethnic groups but not others; dopamine 4 receptor findings have not been replicated or refuted as compared with other polymorphisms

Tender point counts or index

Multiple studies suggesting utility. The tender point count and the tender point index may be influenced by cognitive and emotional aspects of pain, and therefore may be biased

Pressure pain threshold

Multiple studies suggesting utility. The pressure pain threshold may be influenced by cognitive and emotional aspects of pain, which may be minimized by utilizing a random pressure paradigm

Heat and cold pain threshold

Consistently different in patients versus control individuals but not shown to be correlated with changes in clinical pain

Diminished diffuse noxious inhibitory controls

Four cross-sectional studies by different groups suggest utility. Needs further exploration with standardized methods, longitudinal studies

Functional neural imaging

Multiple studies suggesting utility. May be influenced by cognitive aspects of pain. Longitudinal studies needed

Event-related potentials

Reduced P300 amplitude has been noted in three cross-sectional studies by two different groups. Larger studies with standardized methods are necessary. Longitudinal studies needed

Sleep logs and polysomnography

Confirm reports of hypersomnolence, but no changes are pathognomonic of or specific for fibromyalgia

Actigraphy

Inconsistent measure of sleep quality. Report suggesting utility in measuring functional status. Larger, longitudinal studies needed

Hypothalamic–pituitary–adrenal axis

Flattened diurnal cortisol noted in three of four cross-sectional studies by two of three groups. Need to explore influence of biopsychosocial factors. Longitudinal studies needed

Autonomic reactivity

Lower heart rate variability noted in three cross-sectional studies by two different groups. May predispose to condition. Longitudinal studies needed

Autoantibodies

Antiserotonin antibody noted to be increased in three cross-sectional studies by two different groups.

Stringent controls necessary prior to determining utility. Longitudinal studies needed

Neuropeptides

Substance P noted to be increased in cerebrospinal fluid in four cross-sectional studies by various groups.

Potential nonspecific marker of chronic pain

Biochemical and cytokines

Low tryptophan and elevated IL-8 noted. Longitudinal studies needed

Muscle abnormalities

No clear and reproducible abnormality. Additional studies with standardized methods needed