Erythema nodosum (EN), the most form of panniculitis, is mainly caused by numerous infective (especially Beta-hemolytic streptococcal infections) and non-infective (especially sarcoidosis) diseases and drugs. EN associated with vaccines has been rarely reported. We describe herein, an original clinical observation of EN induced by BNT162b2, an mRNA vaccine. A 75-year-old woman presented with diffuse erythematous painful rounded nodular lesions, located symmetrically over her legs. Six days before, she had received the second dose of Covid-19 vaccine (BNT162b2 (Pfizer–BioNTech)), followed by a sudden asthenia, polyarthralgia, throbbing and edema over her lower limbs. She had been given the first dose of the same Covid-19 vaccine 29 days prior to the second without incident. General physical examination was normal. Skin examination showed multiple, erythematous tender, nodules, 10–30 mm in diameter, over the tibial area. Complete blood count, renal and hepatic tests, antistreptolysin O titer, antinuclear antibody, thyroid test and chest radiograph and PCR, were carried out, and found to be normal. Histopathology revealed infiltration of deep dermal vessels and subcutaneous fat with lymphomononuclear cells and neutrophils, consistent with erythema nodosum. Treatment with analgesics led to complete resolution of the lesion after three months. The patient has shown no relapse after follow-up for three months. In conclusion, to our knowledge, this is the first case of EN induced by the second dose of BNT162b2 (Pfizer–BioNTech) Covid-19 vaccine. It is important for clinicians to be aware of this rare, yet potential, adverse effect to this vaccine.
