Translating outcomes from the clinical setting to preclinical models: chronic pain and functionality in chronic musculoskeletal pain

Fibromyalgia (FM) is a chronic pain disorder characterized by chronic widespread musculoskeletal pain (CWP), tenderness, and fatigue, which interferes with daily functioning and quality of life. In clinical studies, this symptomology is assessed, while preclinical models of CWP are limited to nociceptive assays. The aim of the study was to investigate the human-to-model translatability of clinical behavioral assessments for pain and muscle function in a preclinical model of CWP. We assessed correlations between pain behaviors and muscle function in a preclinical model of CWP and in women with fibromyalgia to examine whether similar relationships between outcomes existed in both settings, for usability of clinical assays in model systems. For preclinical measures, the acidic saline model of FM which induces widespread muscle pain, was used in adult female mice. Two gastrocnemius injections of acidic or physiological pH saline were given following baseline measures, five days apart. An array of adapted pain measures and functional assays were assessed for three weeks. For clinical measures, pain and functional assays were assessed in adult women with FM. For both preclinical and clinical outcomes, movement-evoked pain (MEP) was associated with mechanical pain sensitivity. Mechanical sensitivity was correlated to shifts in weight-bearing preclinically and was predictive of functionality in patients. Preclinically, it is imperative to expand how the field assesses pain behaviors when studying multi-symptom disorders like FM. Targeted pain assessments to match those performed clinically is an important aspect of improving preclinical to clinical translatability of animal models.