CASE REPORT:
A 53-year-old man presented with severe pain and soreness in his left upper arm. The pain started 2 days after the first dose of the ChAdOx1 nCoV-19 Corona Virus vaccine into his left deltoid muscle. The pain initially developed in the left upper arm, followed by the right upper arm and bilateral calf muscles (left more than right). The pain gradually increased, and he had difficulty walking and moving his left arm at the time of presentation. He also reported generalised muscle weakness, more pronounced in the proximal upper and lower limbs than the distal ones. There was no history of heavy manual labour or vigorous exercise before the onset of symptoms. There was no malaise or fever. There was no history of any skin rash, breathlessness, dry cough or joint pain. He was non-diabetic and non-hypertensive, with no history of any connective tissue disorders or allergic reactions to drugs or vaccines. There has been no evidence of COVID-19 infection in the past.
On local examination, there was no swelling or erythema. There was tenderness over the left deltoid muscle and bilateral calf muscles, more so on the left side. The MMT score for the left deltoid muscle and left calf muscles was 3/5, and for the same muscles on the right side it was 5/5.
Serologic testing yielded mildly increased serum creatine kinase (187 U/L, reference range 40 – 171 U/L) and alanine transaminase (50 U/L, reference range 10 – 40 U/L) concentrations. Urine analysis excluded myoglobinuria. Initial laboratory findings are summarised in Table 1.
Suspecting skeletal muscle damage, MRI of all the limbs was suggested. At MRI, there was edema in the left deltoid muscle with a thin layer of subfascial fluid adjacent to the muscle belly (Insert Figure 1). Deltoid muscle architecture was preserved. Subtle edema was also noted in the medial head of the left gastrocnemius muscle, with the edema fluid tracking along the intermuscular plane between the gastrocnemius and soleus (Insert Figure 2). No collection or abscess was seen. MRI of the right arm and leg was normal. Based on these findings, a diagnosis of COVID-19 vaccine-associated myositis was made. EMG, muscle biopsy, and immunological workup could not be done as the patient did not give consent.
The patient was advised to rest and take nonsteroidal anti-inflammatory drugs (NSAIDs) for 1 week. Steroids or IVIg were not given, as the symptoms were relatively mild and the liver enzymes were not elevated. On follow-up after 1 week, the pain and tenderness had reduced considerably. The MMT score for the left deltoid muscle and left calf muscle was 5/5. However, the difficulty in walking persisted. Repeat serum creatine kinase after 5 weeks was normal (121 U/L, reference range 40 – 171 U/L). A repeat MRI was not done, as the patient significantly improved after initial management. A timeline of the events following vaccination is given in Table 2.