Widespread pressure pain hypersensitivity at nerve trunks and musculoskeletal structures associated with long-standing unilateral plantar heel pain may result from altered central pain processing, according to a study published in The Journal of Pain.
Although chronic plantar heel pain is often attributed to thickened local fascia, it may also reflect changes in central pain processing.
A total of 35 symptomatic patients (49% women; mean age, 41.7 years; mean body mass index [BMI], 28.6 kg/cm2) and 35 sex- and age-matched healthy controls (49% women; mean age, 40.0 years; mean BMI, 22.9 kg/cm2) were enrolled in this study between January 2017 and February 2018. Bilateral pressure pain thresholds (PPTs) were measured over musculoskeletal points (calcaneus, medial gastrocnemius, tibialis anterior, and second metacarpal) and nerve trunks (median, radial, ulnar, common peroneal, tibial, and sural) in a blinded fashion. A 0 to 10 numeric rating scale was used to assess pain intensity, and the Foot Function Index provided insight into the functional impact of heel pain and related disability. Ultrasound imaging offered precise measurement of plantar fascia thickness.
Statistical analysis revealed that patients with vs without heel pain had bilaterally lower PPTs across local and distant musculoskeletal structures and nerve trunks (P <.001), and that women consistently had lower PPTs compared with men at most anatomic points (P <.001). At the lower extremity peripheral nerve trunks, PPTs were found to be correlated with the disability subscale of the Foot Function Index and with pain intensity at the first morning step (P <.05). Increased fascial thickness was found in participants with heel pain on the affected side compared with the unaffected side, and compared with healthy controls bilaterally (P <.01).
Comparison of PPTs in patients and control individuals indicated large observed effects at nerve trunk and musculoskeletal lower limb locations, where the standardized mean difference ranged from 1.01 to 1.88. Upper limb comparisons revealed moderate observed effects over the nerve trunks (standardized mean difference range, 0.59-0.71).
Study strengths included controlling for BMI and assessing nerve trunk mechanical sensitivity. Study limitations included a cross-sectional design that prevented causal analysis, potential nongeneralizability of results to the wider population with heel pain, only testing pressure pain sensitivity as a static nociceptive pain outcome (vs also using dynamic outcomes), and non-inclusion of additional sensitization process components.
“The presence of widespread pressure pain sensitivity is considered a manifestation of central sensitization….suggesting an altered central nociceptive processing,” concluded the authors. They recommended that future efforts focus on confirmation of this centralization by means of quantitative testing, as well as exploration of the role that nerve trunk tissues play in plantar heel pain pathophysiology.
Plaza-Manzano G, Ríos-León M, Martín-Casas P, Arendt-Nielsen L, Fernández-De-Las-Peñas C, Ortega-Santiago R. Widespread pressure pain hypersensitivity in musculoskeletal and nerve trunk areas as a sign of altered nociceptive processing in unilateral plantar heel pain [published online August 16, 2018]. J Pain. doi:10.1016/j.jpain.2018.08.001