Using multiplexed proximity-extension assays (OLINK, Uppsala, Sweden), the investigators aim to quantify the levels of cytokines and chemokines in the serum of patients with fibromyalgia and in healthy, pain-free controls. FM patients are hypothesized to have an upregulation of cytokines related to B-cell activity, such as CD40 (af Ekenstam et al., 2025).

Using multiplexed proximity-extension assays, the investigators aim to quantify the levels of cytokines and chemokines in the cerebrospinal fluid of patients with fibromyalgia and in control samples from patients that underwent a neurological work-up at the neurological clinic of Uppsala University Hospital. The investigators hypothesize that fibromyalgia patients have upregulated cytokine levels in CSF (Rosenström et al., 2024a), especially regarding e.g. fractalkine, IL8, CCL19, CCL25 - which have previously been found to be upregulated (Bäckryd et al., 2017) and separately been associated with glia cell activity (Maciejewski-Lenoir et al., 1999), BBB permeability (García-Fernández et al., 2023) and fatigue (Rosenström et al., 2025).

The CSF/serum albumin quotient is the gold standard for quantification of blood-brain barrier integrity. The investigators hypothesize that (female) FM patients will have a more permeable BBB, i.e., higher CSF/serum albumin quotient than (female) patients with lumbar disc herniation, degenerative disc disease, osteoarthritis or control patients, suggesting an increased peripheral-central communication, which in turn has been reported to be important for the central immunoenvironment (Rosenström et al., 2025).

QST was used to measure pressure pain thresholds (PPTs), temporal summation and conditioned pain modulation in all FM and HC subjects. FM are expected to have lower PPTs, a stronger temporal summation and impaired descending inhibition compared to HC (Kosek & Hansson, 1997).

All FM and HC participants gave two 4mm punch biopsies of the skin from their right thigh (lateral). These samples will be used to quantify IENFD to be used as a correlation measure with autoantibody titers and inflammatory profiles in serum. The investigators expect reduced IENFD in patients with fibromyalgia (Üçeyler et al., 2013; Evdokimov et al., 2019), and hypothesize that IENFD will be correlated with autoantibody titers.

All FM and HC subjects underwent a one-night ambulatory polysomnography to characterize their sleep quality objectively. The investigators hypothesize that fibromyalgia patients have disturbed overall sleep quality (Muza et al., 2023).

Using rsfMRI, the resting state activity of the brain will be measured in the first 55 FM subjects and in the first 25 HC subjects. We expect a higher functional connectivity in areas related to the default network and lower functional connectivity in areas related to endogenous pain modulation (Cavicchioli et al., 2025).

Using a gadolinium-enhanced, T1-weighted MRI method, the investigators will assess the dynamic permeability of the BBB in the brain of the first 55 FM subjects and the first 25 HC subjects. The investigators hypothesize that FM patients will have a more leaky BBB than controls, as indicated by a faster uptake of gadolinium in the CSF and brain parenchyme. This will be quantified by MRI physicists using standard quantification metrics that mirror physiological function.