Prognostic Value of Measures of the Central Hypersensitivity in Patients With Acute Low Back Pain
Condition: Pain Measurement; Low Back Pain
MeSH terms: Hypersensitivity; Back Pain; Low Back Pain
Study type: Observational

Summary: 
      Background. Patients with chronic low back pain display hyperexcitability of the central
      nervous system (central hypersensitivity). Such hypersensitivity may occur in the acute phase
      and represent a risk factor for the development of chronic pain.

      Objective. To determine the prognostic value of central hypersensitivity for the development
      of chronic low back pain.

      Design. Prospective cohort study.

      Setting. Primary care.

      Patients. 140 individuals with acute low back pain and no history of chronic pain.

      Outcomes. Primary prognostic variable will be the pain tolerance threshold at the second toe
      (the pressure intensity at which a further increase in pressure is deemed intolerable).
      Exploratory secondary prognostic variables are measures of mechanisms related to central
      hypersensitivity: stimulus-specific hypersensitivity (pressure, electrical, heat and cold
      stimulation); tissue-specific hypersensitivity (skin vs. muscle stimulation); localized vs.
      widespread hypersensitivity; spinal cord modulation (electrophysiological measures of
      hypersensitivity and changes in receptive fields); modulation at brain level (descending
      modulation of nociceptive input and cortical plasticity). Clinical primary outcome will be
      the occurrence of chronic low back pain at follow-up.

      Main analysis. The investigators will use least square logistic regression models to
      determine the association of central hypersensitivity with prognosis.

      Relevance. An understanding of the prognostic value of central hypersensitivity may allow an
      early stratification for treatment of individuals at risk of developing chronic low back
      pain. Subgroups of patients may be selected for clinical trials on novel pharmacological
      approaches for the prevention and treatment of central hypersensitivity.
    

Detailed description: 
      Background

      Prolonged afferent nociceptive input induces an increase in the excitability of central
      sensory neurons and plasticity changes that cause hyperexcitability of the central nervous
      system (central hypersensitivity. The hyperexcitable central nervous system amplifies the
      nociceptive signal, thereby producing an exaggerated pain response even in the presence of
      limited tissue damage.

      Using quantitative sensory tests, central hypersensitivity has been detected in different
      chronic musculoskeletal pain syndromes. Patients with chronic low back pain display increased
      pain sensitivity and enlargement of the areas of referred pain after stimulation of tissues
      around and distant from the site of pain (i.e. the leg or the thumb), suggesting that
      widespread central hypersensitivity is associated with this condition. Functional
      reorganization of the cortex has been detected in different pain conditions, including low
      back pain. Using equal levels of sensory stimulation in patients and pain-free controls,
      patients with chronic low back pain showed more extensive patterns of neuronal activation in
      pain-related cortical areas.

      An investigation on patients after a whiplash injury found that those patients with
      persistent moderate or severe symptoms at 6 months had displayed, soon after injury,
      widespread hypersensitivity. Therefore, central hypersensitivity may be an indicator of poor
      prognosis. An acute peripheral lesion may induce plasticity changes leading to central
      hypersensitivity in a subset of individuals. Such a hypersensitivity would facilitate the
      transition from acute to chronic pain and disability. This hypothesis has been investigated
      using a limited number of tests only in a limited number of individuals with whiplash injury,
      but not in any other condition.

      Objective

      To determine the prognostic value of different measures of mechanisms of central
      hypersensitivity in patients with acute low back pain.

      Methods

      140 consecutive Patients with acute low back pain, referred by general practice, will be
      studied prospectively. Primary prognostic variable will be the pain tolerance threshold at
      the second toe (the pressure intensity at which a further increase in pressure is deemed
      intolerable). Exploratory secondary prognostic variables are measures of mechanisms related
      to central hypersensitivity: stimulus-specific hypersensitivity (pressure, electrical, heat
      and cold stimulation); tissue-specific hypersensitivity (skin vs. muscle stimulation);
      localized vs. widespread hypersensitivity; spinal cord modulation (electrophysiological
      measures of hypersensitivity and changes in receptive fields); modulation at brain level
      (descending modulation of nociceptive input and cortical plasticity). Clinical primary
      outcome will be the occurrence of chronic low back pain at follow-up. The investigators will
      use least square logistic regression models to determine the association of central
      hypersensitivity with prognosis.
    

Observational model: Cohort
Time perspective: Prospective
Sampling method: Probability Sample
Study population: 
        Patients with acute low back pain referred from primary care.
      
Keywords: Neuroplasticity; Prognosis