Discussion
The radiation recall phenomenon represents an inflammatory process triggered by different agents in the previously irradiated body area. The most common triggering agents are drugs, especially anti-tumor ones. However, other medications have also been discussed as causes of RRP, including antibiotics 1, simvastatin6, letrozole 7, and tamoxifen8. The inflammation can involve not only the skin but also the lung, esophagus, small intestine, and some other organs.2
The radiation recall phenomenon had not been reported after any vaccination before the COVID-19 vaccination was started. Few reports of RRP after COVID-19 vaccination have been recently published.3-5 The radiation recall dermatitis occurred after the adenovirus vector vaccine (Oxford-AstraZeneca, UK) 5, inactivated virus vaccine (Sinovac Coronavac, China)3, and RNA virus vaccine (Moderna, USA)4. Our case developed radiation recall dermatitis after injection of an inactivated virus vaccine (Sinopharm, China).
The previous cases of radiation recall dermatitis after COVID-19 vaccination presented with well-demarcated, erythematous, and indurated plaques 3 and lesions with marked erythema and dry desquamation 5.
Although only some of the previous cases of radiation recall dermatitis have undergone skin biopsy, some common features are described in the reported cases, including vacuolar changes in the dermo-epidermal junction, apoptotic epidermal cells, vascular dilatation, and dermal infiltration of lymphocytes and eosinophils. 2, 9 The same features were observed in the histopathological examination of our patient.
Ristić hypothesized the role of mast cells in the pathogenesis of RRD.10 Increased number of mast cells in the dermal inflammatory infiltration of our case may favor this hypothesis.
The time-lapse between radiation and RRP in our patient (15 years) was among the most prolonged periods presented in the literature2, but the time between the insult and development of the rash (7 days) was in concordance with most of previous cases.2 The radiation recall rash developed from three hours to five days after COVID-19 vaccine injection. 3-5
The recurrence of RRP on re-exposure with the causative agent is controversial. 1 The reported cases of RRP after COVID-19 vaccination developed the rash either only after the injection of the second dose of vaccine (and not the first dose) or after the first dose and before the injection of the second dose of vaccine3-5; so, the possibility of recurrence on rechallenge was absent or not assessable. Nevertheless, our patient experienced RRP after the injection of both vaccine doses, with a more severe reaction after the second dose.
The radiation recall phenomenon has been treated with oral and/or topical corticosteroids, antibiotics, emollients, and analgesics2, and the rash in our patient improved by a short course of oral and topical steroids.