A Case of Morphea Following Radiotherapy for an Intracranial Tumor: An Example of Isoradiotopic Response.

Sir,

We read with great interest the report recently published in the Indian Journal of Dermatology by Balegar et al.,[1] which describes a case of a 27-year-old male who developed radiation-induced progressive generalized morphea after getting radiotherapy (RT) for an intracranial tumor. In this patient, morphea, initially strictly localized on the irradiated zone, appeared some months after the last cycle of RT, suggesting induction by ionizing radiation.[1]

Radiation dermatitis has for a long time been known to be the most fertile ground for the subsequent development of primary skin cancers on the irradiated area.[2] An irradiated area is prone to the development not only of tumors but also of opportunistic infections and immune-mediated skin disorders (as morphea), depicting a typical example of “immunocompromised cutaneous district” (ICD).[23] Whatever the cause,[2345678910111213141516171819202122232425] the concept of ICD refers to a skin site of locoregional immune dysregulation due to an obstacle to the normal trafficking of immunocompetent cells through lymphatic channels and/or an interference with the signals that the neuropeptides and neurotransmitters, related to peripheral nerves, send to cell membrane receptors of immunocompetent cells. Depending on which of the neurotransmitters and immune cells are involved, this destabilization could be either defective, thus predisposing to infections and tumors, or excessive, thus favoring the occurrence of some immune disorders or dysimmune reactions at the sites “marked” by prior clinical events or injury.[2]

In radiation dermatitis, the lymph network is profoundly disrupted with abnormal dilation of some vessels and obstruction of others, which results in an obvious obstacle to the trafficking of immune cells. Moreover, peripheral nerve fibers are throttled by dermal fibrosis. Therefore, the dysregulation of the immune control occurring in irradiated areas may be explained by the impaired lymph flow on the one hand and the fibrotic throttling or reduction of peptidergic nerve fibers on the other hand. Both changes locally alter the interplay between immune cells conveyed by lymph vessels and neuromediators running along peripheral nerve fibers.[3]

A recent classification of isomorphic and isotopic skin reactions has proposed a newly coined terminology to indicate each specific cause responsible for the occurrence of an ICD and has encompassed additional conditions that had not been defined previously.[1516171819202122232425] According to this new categorization,[25] the report of Balegar et al. can be seen as an example of “isoradiotopic response,” that can be defined as a new skin disease that appears at site of previously diseased or injured (due to a previous irradiation) skin. In this peculiar case, morphea spread and generalized later on the abdomen, chest, and arms.

We thank the authors for giving us the opportunity to discuss such a complex and interesting topic.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.