Fibromyalgia (FM) is not uncommon rheumatologic disease characterized by chronic widespread pain, although the causes underlying this condition remain poorly understood. Recent evidence suggests that malfunctions in the central nervous system resulting in amplification of pain transmission, in combination with environmental factors, may play a role in the etiopathology of FM. Current guidelines for the diagnosis of FM, such as those put forth by the American College of Rheumatology (ACR), are based entirely on clinical features, with no known serological markers available to either confirm or rule out other diseases [1,2]. Variability in the clinical presentation of FM, along with the absence of diagnostic biomarkers, can often result in misdiagnosis, with important consequences on the disease course [3]. Significant overlap is seen between FM symptoms and those of other autoimmune diseases [4]. Among patients with systemic lupus erythematosus (SLE), up to 65% have been shown to meet the ACR criteria for FM [5], which may substantially affect quality of life [6]. Similarly, 57% of patients with rheumatoid arthritis (RA) and 24% of those with psoriatic arthritis exhibit symptoms of FM [7]. Taken together, these studies highlight the difficultly faced by clinicians in trying to differentiate between FM and other autoimmune diseases.

Indirect immunofluorescence (IIF) is one of the most commonly used tests for detection of antinuclear antibody (ANA) on human epithelial type-2 cell (HEp-2) cells, and has recently been recommended as a screening test of autoimmune diseases [8]. In recent years, the IIF assay has been replaced in many laboratories by high throughput and economical screening immunoassays, which incorporate the key autoantibody target antigens into a single assay, on platforms such as enzyme-linked immunosorbent assay (ELISA) and multiplex assays based on addressable laser bead technology [9]. Recognition of nuclear dense fine speckled (DFS) pattern by IIF was initially identified as an atypical ANA pattern in a patient with interstitial cystitis, but have since been linked to a much wider array of conditions [10,11], including chronic inflammatory conditions, cancer, and even certain healthy individuals [10,12,13]. As with other patterns, the typical DFS pattern can vary depending on the manufacturer source of the HEp-2 slides used as substrate [14]. Since a 70-kDa protein was recognized by immunoblotting, the antigen was initially termed dense fine speckled 70 (DFS70) but eventually the primary target autoantigen was identified as the DNA binding transcription coactivator p75 [15]. Anti-DFS70 antibodies can be detected by various technologies including IIF, immunoblot, and ELISA [15].

Although the clinical significance of anti-DFS70 antibodies has been investigated in various autoimmune diseases including RA, SLE, and Sjögren’s syndrome, its prevalence in FM has not been examined [16,17]. Here, we evaluated the clinical significance of anti-DFS70 antibodies in FM, and its association with clinical characteristics.

A total of 75 patients (39 FM, 17 SLE, and 19 HI controls) were enrolled; demographics of the study population are shown in Table 1. The average age was 51.87 ± 11.36 years in the FM group, 37.24 ± 12.13 years in the SLE group, and 48.63 ± 9.42 years in controls (p < 0.001). There were 36 females (92%) in the FM group, 16 (94%) in the SLE group, and 10 (53%) in the control group (p < 0.001). BMI and disease duration were significantly different between the FM and SLE groups.

Anti-DFS70 antibodies were detected at a level of 6.30 U/mL (IQR, 4.722 to 8.435) in the FM group, 4.148 U/mL (IQR, 3.574 to 6.443) in the SLE group, and 5.152 U/mL (IQR, 4.148 to 7.878) in HI controls. These levels were significantly different between the FM and SLE groups (p = 0.008), but not between the SLE group and HI controls (Fig. 1).

No correlation was seen between KFIQ outcomes and anti-DFS70 antibody status (Spearman correlation coefficient r = 0.182, p = 0.268), or between anti-DFS70 antibody status and SF-36 outcomes (r = 0.264, p = 0.104) within the FM group. However, a positive correlation was seen between anti-DFS70 antibody status and VAS (r = 0.589, p < 0.001) (Table 2).

Within the FM group, patients with arthralgia had higher anti-DFS70 antibody values compared to those without arthralgia (p = 0.024); antibody levels were also higher in patients with sleep disturbances relative to those without sleep issues (p = 0.024). Other symptoms, including dry eye, dry mouth, irritable bowel syndrome, Raynaud’s phenomenon, coldness, numbness, depression, and headache were not significantly associated with antibody values (Table 3).

It is now generally accepted that FM is a complex disorder with most experts recommending a multidimensional diagnostic approach including somatic complaints, psychosocial stressors, and psychological factors [19]. Despite improvements to longstanding classification criteria, the modified version of the ACR 2010 for FM is still unable to completely resolve all controversies regarding the diagnosis of FM, due in part to the lack of a reliable biomarker for positive diagnosis or excluding other diseases [20]. Given the variability among methods used to rate severity of FM symptoms, many studies now focus on developing screening tools to enable a definitive diagnose of FM, along with assessments tools that can better rate the severity of FM [21]. Moreover, differential diagnostic tools, including identification of objective biomarkers, are necessary to definitively exclude other autoimmune diseases.

The screening for ANA and other specific autoantibodies has been the standard of the serologic diagnosis for autoimmune diseases. These connective tissue diseases are also called ANA-associated rheumatic diseases (AARD) because of their strong association with ANA [22]. The diagnosis of SLE, Sjögren’s syndrome and systemic sclerosis is highly unlikely in a negative ANA. However, due to a perceived high prevalence of “false negative or positive” results and other technologies for ANA detection continue to evolve the atypical ANA type. In a recent study, the DFS IIF pattern was found in 33.1% of ANA positive HI compared to 0.0% of ANA positive autoimmune diseases (p < 0.0001) [23].

The typical IIF staining pattern against DFS is recognized as fine, uniformly distributed speckles throughout the interphase nucleus and on metaphase chromatin [10,11,24]. As this autoantibody was first detected as a 70 kDa protein by immunoblotting, the antigen was initially termed DFS70, most commonly known as the primary target autoantigen was identified as lens epithelium- derived growth factor or DNA-binding transcription coactivator p75 [10,25]. The anti-DFS70 antibodies have since been detected in a variety of conditions [10,11]. The highest prevalence of anti-DFS70 antibodies has been reported in patients with Vogt-Koyanagi-Harada syndrome (66.7%) and atopic dermatitis (30%), followed by apparently healthy individuals (≤ 10%), while prevalence among patients with autoimmune diseases is significantly lower (≤ 2% to 3%) [10-13,23-29]. An evaluation of more than 10,000 ANA-positive samples by ELISA and immunoblot found that anti-DFS70 antibodies were common among ANA-positive individuals with no evidence of autoimmune disease [27]. Regarding the prognostic and long-term outcomes of HI with positive anti-DFS70 antibodies, the 0 of 40 developed an autoimmune disease over an average of 4 years of follow-up [23]. Therefore, the presence of isolated anti-DFS70 antibodies may be taken as strong evidence against the diagnosis of an autoimmune disease, such as SLE. In our study, anti-DFS70 antibody levels were significantly higher in the HI group than in SLE patients.

In a previous study, upwards of 14% of FM patients were shown to be positive for ANAs, of which 30% had a history of Raynaud’s phenomenon, and 18% had symptoms of Sjögren’s syndrome such as dry eye and dry mouth, but none of these patients progressed to a classic connective tissue disease [30]. FM patients have also been shown to exhibit the same rate of ANA positivity as that of osteoarthritis patients (8.8% and 8.9%, respectively) [31]. Taken together, these studies show that ANAs look as not a good predictor for the differentiation with other connective tissue diseases. The prevalence of anti-DFS70 antibodies and the specificity of these antibodies in FM patients have not been examined. In our study, anti-DFS70 antibody levels were significantly higher in the FM group than in SLE patients, and these antibodies look helpful for differentiating between FM and autoimmune disease.

FM is sometimes related to arthralgia; however, symptoms of arthralgia in FM patients are different from that of arthralgia seen in association with arthritis. In FM patients, pain often appears to be coming from the joints, with many patients reporting symptoms of joint stiffness. However, when the joints of an FM patient are examined by X-ray or other imaging tools, no such damage is evident. While the bones of FM patients are not affected, the soft tissues play an important role in moving a joint, resulting in pain signals from the surrounding muscles and tendons. This type of arthralgic pain must therefore be treated differently than arthralgia due to arthritis. In some FM patients, medications can be directly injected into a painful, stiff muscle to help ease joint pain. Certain pain medications, including those designed to block nerve pain, and antidepressants, also seem to have a positive effect on FM pain. Nonpharmacological interventions, such as lifestyle changes and cognitive-behavioral therapy, including stretching exercises and massage therapy, have also been shown to ease FM arthralgia symptoms.

Insomnia is a common sleep disorder in FM patients. The sleep abnormalities reported in FM patients mainly include a reduction of total sleep time, particularly a decrease in the percentage of slow-wave sleep, along with increased awakenings or arousal. Studies of the microstructure of sleep in FM patients have shown an anomalous intrusion of the alpha rhythm in the slow delta activity, which characterizes deeper sleep stages; a larger number of oxygen desaturations per hour of sleep have also been observed. Furthermore, the Sleep and Pain Diathesis model suggests that sleeping problems may play an important role in the etiology of FM and the persistence of many disease symptoms. Several studies have observed an inverse relationship between sleep disorders and pain thresholds, with those having trouble sleeping more likely to experience widespread pain, fatigue, and negative mood. Given the nature of these symptoms, numerous psychological treatments have been investigated in FM, with several showing improvements in clinical outcomes [32]. In our study, among FM patients, anti-DFS70 antibody levels were positively correlated with VAS scores and were significantly higher in patients reporting symptoms of arthralgia and sleep disturbances. These results suggest that anti-DFS70 antibodies could be correlated with certain cytokine for predicting pain in FM patients. Therefore, anti-DFS70 antibodies may represent an important diagnostic marker for FM without AARD, and be useful for evaluating pain severity in these patients.

As with all research, this study had several limitations. First, the single-center nature of this study limits the extent to which we can generalize these results to other clinics. Second, the small number of FM patients and SLE patients were evaluated without comparisons to other autoimmune diseases such as RA or Sjögren’s syndrome. Further investigation into the role of anti-DFS70 antibodies in more bigger size of FM are necessary to determine the efficacy of using anti-DFS70 antibody levels to predict the severity of FM.