Cutaneous manifestations, present in 16% to 50% of patients with Sjögren syndrome, are considered one of the most common extraglandular presentations of the syndrome. They are classified as nonvascular (eg, xerosis, angular cheilitis, eyelid dermatitis, annular erythema) and vascular (eg, Raynaud phenomenon, vasculitis).9-11 Our patient did not have any of those findings. She had not taken any medications before the rash appeared, thereby ruling out a drug reaction.
The differential for our patient included post–urinary tract infection immune-reactive arthritis and rash, which is not typical with Escherichia coli infection but is described with infection with Chlamydia species and Salmonella species. Moreover, post–urinary tract infection immune-reactive arthritis and rash appear mostly on the palms and soles. Systemic lupus erythematosus–like rashes have a different histology and appear on sun-exposed areas; our patient’s rash was found mainly on unexposed areas.12
Because our patient received the Moderna vaccine 5 days before the rash appeared and later developed swelling of the digits with morning stiffness, a delayed serum sickness–like reaction secondary to COVID-19 vaccination was possible.3,6
COVID-19 mRNA vaccines developed by Pfizer-BioNTech and Moderna incorporate a lipid-based nanoparticle carrier system that prevents rapid enzymatic degradation of mRNA and facilitates in vivo delivery of mRNA. This lipid-based nanoparticle carrier system is further stabilized by a polyethylene glycol 2000 lipid conjugate that provides a hydrophilic layer, thus prolonging half-life. The presence of lipid polyethylene glycol 2000 in mRNA vaccines has led to concern that this component could be implicated in anaphylaxis.6
COVID-19 antigens can give rise to varying clinical manifestations that are directly related to viral tissue damage or are indirectly induced by the antiviral immune response.13,14 Hyperactivation of the immune system to eradicate COVID-19 may trigger autoimmunity; several immune-mediated disorders have been described in individuals infected with SARS-CoV-2. Dermal manifestations include cutaneous rash and vasculitis.13-16 Crucial immunologic steps occur during SARS-CoV-2 infection that may link autoimmunity to COVID-19.13,14 In preliminary published data on the efficacy of the Moderna vaccine on 45 trial enrollees, 3 did not receive the second dose of vaccination, including 1 who developed urticaria on both legs 5 days after the first dose.1
Introduction of viral RNA can induce autoimmunity that can be explained by various phenomena, including epitope spreading, molecular mimicry, cryptic antigen, and bystander activation. Remarkably, more than one-third of immunogenic proteins in SARS-CoV-2 have potentially problematic homology to proteins that are key to the human adaptive immune system.5
Moreover, SARS-CoV-2 seems to induce organ injury through alternative mechanisms beyond direct viral infection, including immunologic injury. In some situations, hyperactivation of the immune response to SARS-CoV-2 RNA can result in autoimmune disease. COVID-19 has been associated with immune-mediated systemic or organ-selective manifestations, some of which fulfill the diagnostic or classification criteria of specific autoimmune diseases. It is unclear whether those medical disorders are the result of transitory postinfectious epiphenomena.5