Capsaicin-Induced Central Sensitization Evokes Segmental Increases in Trigger Point Sensitivity in Humans

This study investigated whether inducing central sensitization evokes segmental increases in trigger point pressure sensitivity. We evoked central sensitization at the C5 segment and validated its presence via mechanical cutaneous sensitivity (brush allodynia) testing. Trigger point pressure sensitivity was quantified using the pain pressure threshold (PPT) value. A 50 cm2 area of the C5 dermatome at the right lateral elbow was pretreated with 45° heat for 10 minutes. Test subjects (n = 20) then received topical capsaicin cream (0.075%; Medicis, Toronto, Canada) to the C5 dermatome, whereas control subjects (n = 20) received a topical placebo cream (Biotherm Massage, Montreal, Canada). PPT readings were recorded from the infraspinatus (C5,6) and gluteus medius (L4,5S1) trigger points at zero (pre-intervention), 10, 20, and 30 minutes after intervention; all PPT readings were normalized to pre-intervention (baseline) values. The difference between the PPT readings at the 2 trigger point sites represents the direct influence of segmental mechanisms on the trigger point sensitivity at the infraspinatus site (PPTseg). Test subjects demonstrated statistically significant increases in Total Allodynia scores and significant decreases in PPTseg at 10, 20, and 30 minutes after application, when compared with control subjects. These results demonstrate that increases in central sensitization evoke increases in trigger point pressure sensitivity in segmentally related muscles.PerspectiveMyofascial pain is the most common form of musculoskeletal pain. Myofascial trigger points play an important role in the clinical manifestation of myofascial pain syndrome. Elucidating the role of central sensitization in the pathophysiology of trigger points is fundamental to developing optimal strategies in the management of myofascial pain syndrome.