A case of wild-type transthyretin cardiac amyloidosis with rheumatoid arthritis

A 72-year-old woman was diagnosed with rheumatoid arthritis (RA) 6 years ago and was referred to our hospital for the management of RA. She achieved remission with methotrexate, and her arthritis was well-controlled. Two years ago, a routine, preoperative check-up revealed left ventricular hypertrophy. One month before the current admission, she experienced worsening heart failure, and echocardiography and other findings suggested cardiac amyloidosis as the underlying cause. She was then admitted to our hospital. Biopsies of both the myocardium and duodenum showed amyloid deposits, and the initial immunohistochemical examination suggested amyloid A (AA) amyloidosis, as the deposits were slightly positive to anti-AA antibody and were sensitive to potassium permanganate pre-treatment. Thus, cardiac and duodenal AA amyloidosis secondary to RA was considered. However, the patient had no renal lesions and her RA was strictly controlled, findings atypical of AA amyloidosis. On repeat immunohistochemical testing, the cardiac and duodenal samples were negative for AA but stained positive for transthyretin (TTR). The diagnosis of a wild-type TTR amyloidosis (ATTRwt) was confirmed on the basis of an absence of the TTR gene mutation. The patient was successfully treated with diuretics and enalapril, and tafamidis (potent and selective TTR stabiliser). A pacemaker was implanted for concomitant complete atrioventricular block. This case is the first reported case of systemic ATTRwt complicated by RA. The treatment strategy for amyloidosis differs greatly depending on the type of amyloid deposition. Therefore, it is important to properly identify the amyloid protein, even if the diagnosis is complicated by RA.