Polymyositis and Polyneuropathy Associated with IgGk Monoclonal Gammopathy in Long COVID

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has led to an increased recognition of its potential to induce neurological complications in the post-infection phase. This paper presents the case study of a 67-year-old male who experienced a severe SARS-CoV-2 infection, followed by the development of myopathy after 11–12 weeks and, subsequently, axonal polyneuropathy associated with IgG monoclonal gammopathies after 30 weeks. Comprehensive laboratory investigations, including serum tests, quantitative electromyography, and muscle biopsies analyzed under light microscopy, were conducted. The patient was followed for a period of 29 months (125 weeks) might offer a more active voice. The investigations unveiled persistent elevations in serum creatine kinase (CK) levels, serum M-protein IgG kappa, myopathic changes in quantitative electromyography, axonal sensorimotor polyneuropathy in nerve conduction studies, and histopathological alterations in muscle biopsies, such as lymphoplasmacytic infiltration and the presence of MHC I, CD4, and CD8 antibodies. Consequently, this paper reviews the clinical and pathological manifestations of polymyositis and polyneuropathy associated with IgG monoclonal gammopathy of clinical significance (MGCS–IgGk polyneuropathy) in the long-term post-COVID-19 period.