MMP3 and polymyalgia rheumatica: For example, in fibromyalgia patients, levels of MMP-3 in cerebrospinal fluid after exercise are negatively correlated with pain thresholds, implying that MMP-3 may play a promoting role in pain perception in fibromyalgia.[8] Additionally, serum MMP-3 levels are elevated in inflammatory rheumatic diseases, especially polymyalgia rheumatica.[9] However, these studies are susceptible to confounding factors and cannot clarify the directionality, which hinders the exact determination of the causal relationship between MMP-3 and fibromyalgia.