Anti-MDA5 (Melanoma differentiation-associated protein 5) myositis is a rare subtype of dermatomyositis (DM) characterized by distinct ulcerative, erythematous cutaneous lesions and a high risk of rapidly progressive interstitial lung disease (RP-ILD). It has been shown that SARS-CoV-2 (COVID-19) replicates rapidly in lung and skin epithelial cells, which is sensed by the cytosolic RNA-sensor MDA5. MDA5 then triggers type 1 interferon (IFN) production, and thus downstream inflammatory mediators (EMBO J 40(15):e107826, 2021); (J Virol, 2021, https://doi.org/10.1128/JVI.00862-21 ); (Cell Rep 34(2):108628, 2021); (Sci Rep 11(1):13638, 2021); (Trends Microbiol 27(1):75–85, 2019). It has also been shown that MDA5 is triggered by the mRNA COVID-19 vaccine with resultant activated dendritic cells (Nat Rev Immunol 21(4):195–197, 2021). Our literature review identified one reported case of MDA5-DM from the COVID-19 vaccine (Chest J, 2021, https://doi.org/10.1016/j.chest.2021.07.646 ). We present six additional cases of MDA5-DM that developed shortly after the administration of different kinds of COVID-19 vaccines. A review of other similar cases of myositis developing from the COVID-19 vaccine was also done. We aim to explore and discuss the evidence around recent speculations of a possible relation of MDA5-DM to COVID-19 infection and vaccine. The importance of vaccination during a worldwide pandemic should be maintained and our findings are not intended to discourage individuals from receiving the COVID-19 vaccine.

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IntroductionMulticentric reticulohistiocytosis (MRH) is a rare disease that is known to affect the skin and joints, primarily. It is considered a rare form of non‐Langerhans cell histiocytosis (Group C) that can cause destructive inflammatory arthritis involving both the small and large joints. Cutaneous eruptions of periungual, “coral beads” and nodules appearing over the distal fingers are considered pathognomonic clues for identifying this disorder. Histology evaluation of the cutaneous papules typically shows infiltrative histiocytes and multinucleated giant cells. Although no well‐established therapies exist to date, a variety of immunosuppressants have been used with varying degrees of success.Case DescriptionA 53‐year‐old Caucasian female patient with a family history of rheumatoid arthritis and a personal history of Sjogren's syndrome presented to the rheumatology clinic complaining of pain in her bilateral hands and fingers. There were several small, papulo‐nodular lesions ranging from 1 to 2 mm in size noted at the base of her nails. A 4 mm punch biopsy of one of the papules from the neck showed dermal infiltration of eosinophilic mononucleated and multinucleated giant cells with “ground glass” appearing cytoplasm consistent with MRH. X‐ray of her hands showed periarticular demineralization and erosions surrounding several bilateral proximal and distal interphalangeal joints, and thus tofacitinib in addition to methotrexate, hydroxychloroquine, and dexamethasone (dosed weekly) was started to help control any further articular damage.ConclusionOur aim is to further support the relation of MRH with autoimmune diseases, including Sjogren's syndrome. Autoimmune diseases have been reported in association with MRH, although a clear association has yet to be made.