Four cases of dermatomyositis with abnormally high anti-MDA-5 antibody titres and not high levels of serum ferritin.

Anti-melanoma differentiation-associated gene 5 (MDA-5) antibody-positive dermatomyositis is a fatal disease presenting with rapidly progressive interstitial lung disease. High ferritin levels are a well-known poor prognostic factor. A high anti-MDA-5 antibody titre was also recently identified as a poor prognostic factor. We encountered four cases that had extremely high anti-MDA-5 antibody titres without high levels of ferritin in the initial examination. All cases were female with ages ranging between 29 and 54 years (mean age, 44 years). In the initial examination, anti-MDA-5 antibody titres were 2060-3040 (normal range, <32 index), ferritin levels were 87-480 ng/ml (normal range, 2.6-129.4 ng/ml), KL-6 level was 186-1806 U/ml (normal range, <500 U/ml), and creatine kinase level was normal in all patients. One patient had respiratory distress on exertion. Computed Tomography (CT) images showed mild ground-glass attenuation/reticular shadows near the pleura in all patients. Three patients were treated with a combination of high-dose glucocorticoids, intermittent intravenous cyclophosphamide, and calcineurin inhibitors, and two required plasma exchange due to the worsening of lung lesion. In these patients, ferritin and KL-6 levels tended to elevate after the beginning of treatment. Very mild pulmonary lesions disappeared in one patient treated with moderate doses of a glucocorticoid and calcineurin inhibitor. All patients survived, and one required oxygen on exertion at discharge. The condition of patients with abnormally high anti-MDA-5 antibody titres may deteriorate even though ferritin levels were not high and lung shadows are minimal at presentation. Therefore, intensive treatment needs to be considered early in the course of the disease regardless of the serum ferritin level.