Abstract
Background IMPP have myopathological features that are distinct from dermatomyositis (DM) and are usually associated with extramuscular manifestations.1 2 There is also some evidence that the pathophysiology in Anti-Mi-2 DM may be more similar to phenotypes with IMPP than DM associated with other myositis antibodies.3
Methods/Results We present a case of a 71-year-old woman with a six-month history of progressive muscle weakness. Her father had Paget’s disease of the bone and Dementia in his 70’s. Examination revealed distal weakness in the upper limbs including the deep finger flexors and proximal weakness in the lower limbs. She also had oropharyngeal dysphagia and axial weakness. There were no nailbed or skin changes. Investigations revealed creatinine kinase level of 3579U/L, anti-nuclear antibody of 1:2560 with positive Mi-2a and Mi-2b antibodies. Nerve conduction studies were normal. Electromyography revealed mixed myopathic and neurogenic motor unit potentials in weak muscles with fibrillation potentials. Muscle biopsy of the left vastus lateralis showed features of a chronic immune mediated myopathy consistent with a chronic IMPP. Given her atypical presentation and family history of Pagets disease, Pathwest comprehensive neuromuscular genetic panel was also sent off. Extensive evaluation including FDG-PET was negative for any malignancy. She was treated with a combination of intravenous methylprednisolone and immunoglobulin. After two months of treatment the patient remained similarly disabled.
Conclusions This case highlights the clinical and pathological heterogeneity that can be seen in patients with acquired immune and inflammatory myopathies and provides further evidence of the overlap between IMPP and Anti-Mi-2 DM.
References
Pestronk A. Acquired immune and inflammatory myopathies: pathologic classification. Curr Opin Rheumatol 2011;23:595–604
Bucelli RC, Pestronk A. Immune myopathies with perimysial pathology. Clinical and laboratory features. Neurology: Neuroimmunology and Neuroinflammation 2018;5(2):e434
Tanboon J, Inoue M, Hirakawa S, Tachimori H, Hayashi S, Noguchi S, Suzuki S, Okiyama N, Fujimoto M, Nishino I. Pathologic Features of Anti-Mi-2 Dermatomyositis. Neurology. 2021;96(3), e448–e459.
