A case of rheumatoid arthritis complicated with mucous membrane pemphigoid

Rheumatoid arthritis (RA) is a disease of unknown aetiology that causes irreversible joint destruction and has been known to present with not only various extra-articular symptoms, but also various autoimmune disorders. Mucous membrane pemphigoid (MMP) is a chronic autoimmune disease characterised by inflamed and eroded mucosa. The prognosis of MMP can be poor, so early diagnosis and prompt initiation of therapy are necessary for optimal management. Here, we report a rare case of RA complicated with MMP involving a 68-year-old woman admitted to our hospital because of hoarseness and symmetrical narrowing of the eye fissures. She presented with bilateral coxalgia and had been diagnosed with RA 24 years earlier. Oral methotrexate was prescribed, but subsequently discontinued, and this was followed by treatment with tocilizumab 3 years earlier. Tocilizumab was discontinued because of financial distress 5 months earlier, after which her RA disease activity worsened. She presented to our hospital after further worsening of her eye-opening difficulty. Physical and laboratory examinations led to a diagnosis of MMP. Her sputum, cough, throat discomfort, conjunctival congestion, mucous erosion, and blistering promptly disappeared after treatment with rituximab (500 mg per week for 4 weeks). She subsequently recovered her vocalisation ability, and her hoarseness, dysphagia, and eye-opening difficulty gradually improved, but not completely. This case suggests that that RA and MMP share common immunological mechanisms. Therefore, MMP should be considered when encountering patients with RA who present with systemic membrane mucous disorders.