NextGenPath Diagnostics

Anti-Mi-2 Autoantibody Associated DM

Dermatomyositis (DM) is a heterogeneous IIM with a gamut of demographic, clinical, laboratory, and myopathological features.
The autoantibodies observed in DM are directed against various intracellular molecules, viz., Mi-2, MDA5, SAE, NXP2, and TIF-1γ.
Mi-2 autoantibodies were first identified in 1976, in the serum of a 60-year-old woman with features of DM (patient Mi).
Mi-2 protein is an integral part of the nucleosome remodeling deacetylase (NuRD) complex that carries out both ATP-dependent chromatin remodeling and histone deacetylase activities.
The characteristic presentation of anti-Mi-2 DM is proximal muscle weakness associated with skin lesions.
Typical skin findings include Gottron papules, heliotrope rash, and shawl sign.
Other than the skin and muscle, generally no other organ involvement is seen.
Serum creatine kinase (CK) values are usually very high.
Biopsy: Shows marked myofiber size variation, perifascicular atrophy with accompanying necrotic myofibers and myophagocytosis . Inflammation is typically intense and diffuse comprising of lymphocytes and macrophages distributed in the perimysium and endomysium. MHC class I immunostaining highlights the perifascicular accentuation gradually losing the intensity toward the center of the fascicle. Membrane attack complex (C5b-9) immunostaining is found on the sarcolemma and less frequently on the capillaries.
Data with respect to the association between anti Mi-2 antibodies and malignancies is controversial.

Gaspar BL, Vasishta RK, Radotra BD. Myopathology: A Practical Clinico-Pathological Approach to Skeletal Muscle Biopsies. Springer Nature: Singapore, 2019.