Prominent mitochondrial pathology in a case of refractory dermatomyositis: coincidence or concause?

Introduction: Mitochondrial alterations are a common finding in muscle biopsy of sporadic inclusion body myositis (s-IBM) and polymyositis with mitochondrial pathology (PM-Mito). Both disorders generally have poor treatment response. Nevertheless, mitochondrial myopathology has been rarely reported in dermatomyositis (DM) outside areas of perifascicular atrophy and a relationship with therapeutic outcome is not established. Methods: We report on clinical, immunological, radiological, and myopathological findings of a case of severe, treatment-refractory anti-Mi-2-positive DM. Results: A 77-year-old woman developed anti-Mi-2 DM with severe diffuse muscle weakness associated with abundant mitochondrial abnormalities at muscle biopsy, beside the typical features of inflammatory myopathy. The patient was poorly responsive to multiple-line therapies and finally anti-JAK (anti-Janus activated kinase) was administered, leading to partial clinical improvement. Discussion: Given the usual satisfactory treatment response and favorable outcome of anti-Mi-2 DM, we suppose that mitochondrial dysfunction on muscle biopsy could represent a marker of disease severity in DM, predicting a worse response to treatment and a poor clinical outcome. JAK-inhibitors could represent a good treatment option in refractory anti-Mi-2 DM with mitochondrial abnormalities.