Pain problems were prevalent in ILD patients but only few studies were carried out this problem. It is the first time that study were carried on to measure pain problem in ILD patients by SF-MPQ and a healthy control group, persons of similar age and gender without lung disease, was set in order to explore the characteristics of pain in ILD patients. In our present study, these findings indicate that pain problem is more prevalent in ILD patients. The main pain location in ILD patients was chest, joint and limb. The intensity of pain may be related to age, exposure history, mMRC score and DLCo, % of predicted. Compared to ILD patients with no-pain, patients with pain also experienced impaired healthy statues both physically and mentally, which might be predominantly caused by more limitations in daily functional.
Significant pain is not considered a typical feature of ILD. However, pain was common in both IPF and non-IPF ILDs, and the prevalence of this deficit was higher compared to the rates found in healthy controls. ILD group experienced higher pain intensity than HC group both in feeling and emotion dimension. Prevalence of pain was found higher in ILD compared to the general population(28,29). As was showed in our study more than half ILD patients(39/63) suffered pain in their daily life. We also noted that in the ILD individuals, the main pain locations were chest (46.2%) and joint (23.1%) among all ILD patients with pain. 57.1% IPF patients with pain declared having chest pain, which was higher than non-IPF(40.0%). Kaisa’s study (7) also found that 31.2% (79/253) IPF patients experienced chest pain. But a British study (30) about 111 patients with fibrotic ILD found that most frequently reported painful areas of this subjects were the back (34%) and lower limbs (25%), and they were similar comparing IPF and non-IPF patients. According to literatures about pulmonary disease, the causes of chest pain remain unclear which can be related to pulmonary loss of elasticity of the parietal pleura, pathological bronchial fibrosis, thoracic vertebral deformity, costotransverse, intervertebral arthropathy and activities related to breathing and postural dysfunction (31,32). The incidence of joint pain in patients with CTD-ILD was higher than patients with IPF in our study, which was in line with the previous studies(33). It was reported that the prevalence of joint pain in CTD-ILD patients could be explained by the high anti-cyclic citrullinated peptide antibody (anti-CCP) positivity in patients(34). Further studies with larger sample sizes are required to confirm these findings.
Higher intensity of pain in ILD patients was also associated with many factors in our study, included younger age (< 60 years), exposure history of ILD risk factors, longer distance of 6MWD(≥ 250 m), higher mMRC score(2–4) and lower DLCo, % predicted, impaired SF-36 and HAD score. When undergoing severe dyspnea, patients normally gave an extra worse result of pulmonary function test, especially FVC, % predicted and DLCo, % predicted, and unsatisfied 6WMT, a practical and reliable measure of exercise tolerance that is widely used to assess the functional status of patients with IPF(35), which show the severity of the patient's current condition and reflect the current quality of life(36–38). It was reported in previous studies that the association between dyspnea severity in mMRC score and intensity of pain was reported in the previous studies(7,10), and the prevalence of chest pain in IPF patients had a positive linear relationship to increased mMRC score (7). In our study, compared to ILD patients without pain, the ILDs with pain did have lower DLCo pred % and higher mMRC score. Moreover, according to the results of MPQ, the pain intensity in ILD patients was greatly infected by the DLCo, % predicted and dyspnea severity. But we didn’t see the relationship of pain intensity in ILD patients with the 6MWT SpO2 and FVC, % predicted. The apparent paradoxical relationship between pain and lung function was also reported in lots of pain studies in COPD studies(12,39,40). This inverse relationship, probably also caused by selection bias, also can be interpreted that other symptoms like dyspnea were more distressing than pain, leading to more focus on dyspnea and less on pain, also causing patients to be reluctant to spontaneously report pain(41–43).
ILD Patients with pain also suffer worse quality of life and psychological deficits, like symptoms of anxiety and depression, . The impaired HRQoL, according to results of SF-36, except for the poor total score, mainly performed on mental health, bodily pain, vitality and role emotional, which was reflected in the results of SF-MPQ and HADs. We further found the pain intensity related to the degree of depression and anxiety. In addition to increasing dyspnea, many of the ILDs, such as sarcoidosis and connective tissue disease ILDs, are associated with extrapulmonary manifestations that may also lead to pain and add tremendous burden on HRQoL and mental health. Ryerson et al(9) reported the novel finding that baseline pain severity was associated with baseline depression score and particularly in the non-idiopathic pulmonary fibrosis population. Therefore, those indicated the need for healthcare providers, clinicians, and patients to pay greater attention to ILD patients with pain and consider strategies to minimize their impact on patients’ quality of life, healthcare utilization, and prognosis.
To our knowledge, this is the first study to investigate pain in patients with ILD including the intensity, location, type and associated factors. However, generalizability beyond this specific group and setting is limited, as only 126 participants from one hospital were included. There are some limits in our study results to a single time-point and does not allow us to describe the changes in pain or symptoms over time. Our study may be subjected to some selection bias and, as some patients at a very advanced stage of the disease or close to death were likely to be lost from the cohort. Possibilities of false negative due to small sample size and false positive due to multiple testing. Another limitation is that the score of those questionnaire may be mixed with subjective feeling ,especially the VAS score, and effected by individual verbal comprehension. The last but not the least, what were the accurate causes of pain in ILD patients couldn’t be completely sure in our study. In the future, a larger sample of cross- sectional or cohort studies may be conducted on factors related to pain intensity to further verify these results.