Background Fibromyalgia syndrome (FM) is a chronic pain disorder characterised by symptoms of morning stiffness, fatigue, depression, non-restorative sleep and reduced cognitive performance, some of which are worsened by emotional distress, meteorological changes, insomnia and strenuous activity.Some of the patients' symptoms, as well as their physical and psychological characteristics, can be attributed to autonomic nervous system (ANS) dysfunction. It has been demonstrated that ANS dysfunction in patients with type 1 diabetes mellits can induce functional alterations in the regulation of pulmonary microvascular tone and the distribution of pulmonary blood filling.

Objectives The aim of this study was to evaluate whether pulmonary diffusing capacity is impaired in patients with FM as it is in those with other diseases characterised by ANS dysfunction such as type 1 diabetes.

Methods Forty-five consecutive anti-nuclear antibody (ANA)-negative female Caucasian patients aged 50.1±5.6 years with FM and compared with 45 healthy female control volunteers matched in terms of age and body mass index (BMI). The autonomic function have been evaluated by means of standard electrocardiography (ECG), finger blood pressure respiration, and muscle sympathetic nerve activity (MSNA) at rest and during a stepwise tilt test up to 75°. Their autonomic profiles were drawn up on the basis of MSNA, plasma catecholamine levels, and spectral indices of cardiac sympathetic and vagal modulation, and sympathetic vasomotor control computed by means of the spectrum analysis of RR and systolic arterial pressure (SAP) variability. Lung volumes and dynamic spirometry parameters were assessed by means of plethysmography. All the patients were clinical evaluated and completed the fibromyalgia impact questionnaire (FQI) and Compositive Autonomic Symptom Score (COMPASS) questionnarie.The number of tender points (TPs) was counted using Wolfe's protocol, which gives a total score of 0–18, and the intensity of somatic pain was assessed using a 100 mm visual analogue scale (VAS).The severity of Raynaud's phenomenon was evaluated using the Raynaud's Condition Score (RCS), an ordinal scale ranging from zero to10 that measures the level of difficulty experienced by patients.

Results There was no difference in lung volumes between the FM patients and healthy controls, but the carbon monoxide diffusion capacity of the lung (DLCO) (83±4 vs. 96±5; p<0.001), Kco (84±5 vs 98±5; p<0.001), alveolar-capillary membrane (DM) (12.7±2.4 vs 13.6±1.8; p<0.05) and pulmonary capillary blood volume (Vc) (48±3.9 vs 65±7; p<0.001) were significantly reduced in the patients.The COMPASS-31, RCS and pain VAS scores significantly correlated with DLCO, alveolar-capillary membrane (Kco) and Vc with the correlation being particularly close in the case of Vc. Furthermore, univariate Cox proportional hazard analysis showed that the three scores were all significantly associated with an increased risk of impaired DLCO (respectively, χ² 16.21, p<0.0005; χ² 7.09, p<0.005; χ² 6.37, p<0.01).

Conclusions FM impairs DLCO mainly as a result of a reduction in Vc, and that this defect is inversely proportional to the severity of the dysfunction suggestiong a relationship between impaired DLCO and autonomic nerve dysfunction.

Disclosure of Interest None declared