Unmet Needs and Current Challenges of Rheumatoid Arthritis: Difficult-to-Treat Rheumatoid Arthritis and Late-Onset Rheumatoid Arthritis.

Despite remarkable advances in the management of RA, there are still unmet needs that rheumatologists need to address. In this review, we focused on difficult-to-treat RA (D2T RA) and late-onset RA (LORA), and summarized their characteristics and management. The prevalence of D2T RA is reported to be 6-28% and many factors have been identified as risk factors for D2T RA, including female sex, long disease duration, seropositivity for rheumatoid factor and anti-cyclic citrullinated peptide antibody and their high titer, baseline high disease activity, and comorbidities. D2T RA is broadly divided into inflammatory and non-inflammatory conditions, and clinical features differ according to background. A proportion of D2T RA can be managed with treatment modification, mainly with interleukin-6 receptor inhibitors or Janus kinase inhibitors, but some D2T RA patients have a poor prognosis; thus, the implementation of precision medicine by stratifying patients according to disease status is needed. In the aging society, the epidemiology of RA is changing and the prevalence of LORA is increasing worldwide. LORA has distinct clinical features compared with young-onset RA, such as acute onset, low seropositivity, and high inflammation. The pathogenesis of LORA remains to be elucidated, but proinflammatory cytokines, including interleukin-6, have been reported to be significantly elevated. LORA has several management concerns other than RA itself, such as geriatric syndrome and multimorbidity. The treat-to-target strategy is effective for LORA, but the evidence is still lacking; thus, it is important to accumulate clinical and related basic data to establish the optimal treatment strategy for LORA.