Fibromyalgia in Patients With Hidradenitis Suppurativa

Pain is a paramount and debilitating symptom of hidradenitis suppurativa (HS). However, clinical experience reveals that pain intensity is not always consistent with disease severity, and pain can persist after disease remission.1 In other HS-associated inflammatory diseases in which this phenomenon was previously observed, an increased prevalence of fibromyalgia (characterized by generalized entheseal pain) was described.2 In HS, more than half of patients exhibit tenderness of the entheses.3 Therefore, we conducted this study to assess fibromyalgia prevalence using the 2016 Fibromyalgia Diagnostic Criteria in patients with HS compared with age- and sex-matched controls.4

Methods:

We performed a cross-sectional, survey-based, case-control study at the Department of Dermatology, Erasmus University Medical Center Rotterdam, between February and November 2020. The Erasmus University Medical Center Rotterdam Ethical Committee confirmed that the Medical Research Involving Human Subjects Act did not apply to this research. All patients provided written informed consent. We followed the STROBE reporting guideline.

All consecutive patients with HS 18 years or older were included during routine clinic visits. Age- and sex-matched controls (with non–pain-related conditions) were recruited from the same outpatient clinic. Fibromyalgia was diagnosed according to the 2016 Fibromyalgia Diagnostic Criteria.4 Univariate and multivariate logistic regression models were constructed to assess the outcomes of variables associated with fibromyalgia.

Two-sided P ≤ .05 was considered statistically significant. Statistical analyses were performed from December 2022 to January 2023, using SPSS Statistics 26.0 (IBM Corporation). The eMethods in Supplement 1 provide more details.

Results:

The study included 100 patients with HS (median [IQR] age, 34.5 [27.3-47.0] years) and 100 controls (median [IQR] age, 33.5 [27.0-48.8] years), and both groups comprised 71 females (71%) and 29 males (29%). Table 1 shows characteristics of each group. No significant difference in self-reported fibromyalgia diagnosis was found between the groups. However, significantly more patients with HS than controls were diagnosed with fibromyalgia when the diagnostic criteria were used (13 [13%] vs 4 [4%]; P = .02).

Univariate logistic regression of all participants identified a significantly increased odds ratio (OR) for fibromyalgia in patients with HS (3.56; 95% CI, 1.13-11.41; P = .03), rheumatoid arthritis (5.97; 95% CI, 1.01-35.29; P < .05), and previously diagnosed depression (7.75; 95% CI, 2.68-22.39; P < .001) (Table 2). Rheumatoid arthritis, another possible risk factor for fibromyalgia, was included in the multivariate logistic regression. The OR for fibromyalgia among patients with HS remained significantly increased at 3.45 (95% CI, 1.08-11.09; P = .04). Within the HS group, both the International Hidradenitis Suppurativa Severity Score System (OR, 1.11; 95% CI, 1.03-1.20; P = .01) and pain (OR, 1.47; 95% CI, 1.15-1.87; P = .002) scores showed an association with fibromyalgia and hence increased odds.

Discussion:

Two studies have described fibromyalgia prevalence in patients with HS.5,6 The first was a cross-sectional population-based study with 56 084 patients that found increased fibromyalgia odds (1.51) in patients with HS. The second study was a retrospective medical records review with 1356 patients that found the fibromyalgia prevalence in the HS population was lower than the overall US estimated prevalence (3.2% vs 6.0%).5,6 However, both studies relied on self-reported fibromyalgia diagnoses. In the present cohort, the actual odds for fibromyalgia were 3 times higher than the self-diagnosed reports, highlighting the limitations and underestimation associated with self-reported fibromyalgia diagnoses in research settings.

Proinflammatory cytokines, which are elevated in HS, such as tumor necrosis factor and interleukin 17 are also increased in plasma of patients with fibromyalgia. This mechanism suggests that elevated levels of proinflammatory cytokines might be associated with increased fibromyalgia prevalence, strengthening the hypothesis that local and systemic inflammation could drive the alteration in neurotransmission.

A study limitation was the single-center design, which could have created a homogeneous population and may limit generalizability. However, a study strength was use of the 2016 Fibromyalgia Diagnostic Criteria vs self-reported diagnosis. Antidepressants and antiepileptics, such as gabapentin and pregabalin, could be beneficial in treatment of chronic pain for patients with HS and comorbid fibromyalgia. This case-control study found that patients with HS had over 3 times the odds of having fibromyalgia compared with controls according to the 2016 Fibromyalgia Diagnostic Criteria.