[Assessment of muscle pain and hyperalgesia. Experimental and clinical findings]

It is evident that muscle hyperalgesia and referred pain have an important role in chronic musculoskeletal pain. More knowledge of the basic mechanisms involved and better methods of assessing muscle pain in clinical practice are needed so that treatment regimens can be revised and improved.

Methods of quantitative sensory testing of muscle pain and associated phenomena are described. These methods make it possible to evaluate manifestations of muscle pain in a standardised way both in patients suffering from musculoskeletal pain and in healthy volunteers.

Elevated muscle sensitivity becomes manifest as (1) pain evoked by a normally non-noxious stimulus (allodynia), (2) abnormally intense pain evoked by noxious stimuli (hyperalgesia), or (3) unusually large areas of referred pain with associated somatosensory changes. These changes can occur as increased somatosensory sensitivity of deep somatic tissues or of the skin in areas of pain referral. Some manifestations of sensitisation in chronic musculoskeletal pain patients, such as expansion of the areas of referred muscle pain, can be explained by the extra segmental spread of central sensitisation seen in animal experiments.

An important part of the manifestations of pain in chronic musculoskeletal disorders may be due to peripheral and central sensitisation processes, which are also involved in the transition from acute to chronic pain. Knowledge of these processes has expanded enormously in recent years; it should be utilised when new intervention strategies are designed.