DISCUSSION:
ChAdOx1 nCoV-19 is a recombinant, replication-deficient chimpanzee
adenovirus vector which encodes the SARS-CoV-2 Spike (S) glycoprotein.
When administered, it causes the genetic material of part of the
coronavirus to be expressed, thereby stimulating an immune response.
Direct inoculation of vaccine via an intramuscular route exposes the
muscle to these modified contaminant agents and elicits an immune
response to the antigen injected [7].
Autoimmunity associated with vaccines can be attributed to the
cross-reactivity between antigens or to the effect of adjuvants [8].
ASIA (Autoimmune/inflammatory Syndrome Induced by Adjuvants) is a
complex entity referring to the autoimmune manifestations that appear to
be caused by adjuvants and may be related to specific HLA phenotypes,
the development of autoantibodies, or even evolve into a rheumatological
disorder [9]. ASIA is characterised by inflammatory musculoskeletal,
neurocognitive, and/or constitutional symptoms on exposure to an
external stimulus and improves when the stimulus is withdrawn[9].
Recently, Das et al.[10] have reported a case of ASIA syndrome
following the first dose of the ChAdOx1 nCoV-19 vaccine in a 47-year-old
patient, manifesting as subacute thyroiditis.
It is known that COVID-19 can lead to myositis and rhabdomyolysis due to
immune hyperactivation and excessive cytokine release[11]. The
antibodies against SARS-CoV-2 spike glycoproteins cross-reacting with
structurally similar host proteins (molecular mimicry) have been
suggested as a possible cause for this acute autoimmune response. Other
proposed mechanisms include cytokine-mediated autoinflammation, CD8
T-cell overactivation, formation of antigen-antibody complexes, and
structural deformity of myocytes caused by intake of viral
antigen[11]. It has been suggested that the COVID-19 vaccination
could also trigger such a response[12]. However, the exact mechanism
remains unclear. The clinical features suggestive of COVID-19-induced
myositis include proximal muscle weakness, myalgia, features of muscle
inflammation in MRI, dermatomyositis, and rhabdomyolysis evidenced by
elevated CK and myoglobinuria[11].
Theodorou et al.[7] have reported a case similar to ours, with a
56-year-old woman presenting with myalgia and progressive muscle
weakness that started 8 days after the second dose of COVID-19
vaccination. As opposed to our case, the symptoms were limited to the
left upper arm, where the vaccination was given. Myositis was diagnosed
based on elevated CK and typical MRI findings. Maramattom et al.[1]
have recently reported three similar cases, all of which showed features
of inflammatory myositis on MRI, while one patient showed features of
vasculitis in addition to myositis on biopsy.
CK levels in myositis are variable. Though CK levels are raised in most
cases of inflammatory myopathy, they may be minimally elevated or even
normal in some cases like inclusion myositis. Although injection site
myositis has been reported following various vaccinations, it is usually
associated with elevated CK. Our case showed myositis in the injection
site and in other muscles following the COVID-19 vaccine, though CK was
only mildly raised, with radiologic evidence of myositis and
considerable patient symptoms and activity limitation. This merited
medical attention since ChAdOx 1 nCoV 19 is a newly developed vaccine
that is under Emergency Use Authorization.
Although muscle biopsy was not performed in our patient, the temporal
link between the vaccination procedure and the patient’s symptoms,
imaging features, the reversible nature of symptoms, and lack of
alternative cause suggests a diagnosis of COVID-19 vaccine-associated
myositis as the cause. In addition, the other possible causes of muscle
edema, like trauma, infection, neoplastic infiltration, and infarction
(as in microvascular disease like diabetes mellitus), were not present
in this case. Though the symptoms were mild, they incapacitated the
patient for some time, resulting in a loss of work days, which was
relieved with rest and NSAIDs, not requiring treatment with steroids.
Hence, we are reporting this case, which might lead to the formulation
of newer studies to look into the mechanistic pathways of COVID-19
vaccine associated myositis.