In the current study, the overall prevalence and the main underlying etiologies of inflammatory
low back pain (
ILBP) were determined, and the effectiveness of treatment with
sulfasalazine was investigated in patients with inflammatory versus
mechanical low back pain (LBP). In a prospective study conducted from July 2013 until August 2015, 1,779 consecutive patients within the age range of 18-50 years with a primary complaint of LBP referring to the rheumatology clinics were included. The patients were classified into two distinct groups: those suffering from
ILBP (n=118) and those having mechanical LBP (n=1,661). Patients were followed-up for assessing the response rate to
sulfasalazine with a mean follow-up time of 16 months. Results showed that among the total number of participants, 6.6% suffered from
ILBP. The main underlying diagnoses of
ILBP were undifferentiated
spondyloarthropathy (USpA) (61.0%) and
ankylosing spondylitis (24.6%). During the follow-up period, 3.4% of the participants had an appropriate response to only nonsteroidal anti-inflammatory drugs, 57.6% to
sulfasalazine, 26.3% to addition of
methotrexate to the previous regimen, and 12.7% to
biological agents. Multiple logistic regression results showed that the underlying disease had a significant effect on the
sulfasalazine response. The odds for response to treatment was 3.53 times higher in USpA patients compared to other patients (odds ratio =3.53, 95% confidence interval: 1.63-7.68, P=0.001). In 69.4% of the participants, the highest response to
sulfasalazine was found, which was related to the underlying USpA. This study found that an adequate response to nonsteroidal anti-inflammatory drugs in patients with
ILBP was potentially increased by adding
sulfasalazine. Thus, the observed response rate was dependent on the nature of underlying
spondyloarthropathy.