Indian Journal of Dermatology
: 2012  |  Volume : 57  |  Issue : 6  |  Page : 498--499

The remarkable paradigm of segmental (mosaic) drug eruptions

Daniele Torchia 
 Via della Scala 58, 50123 Florence, Italy

Correspondence Address:
Daniele Torchia
Via della Scala 58, 50123 Florence

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Torchia D. The remarkable paradigm of segmental (mosaic) drug eruptions.Indian J Dermatol 2012;57:498-499

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Torchia D. The remarkable paradigm of segmental (mosaic) drug eruptions. Indian J Dermatol [serial online] 2012 [cited 2021 Mar 7 ];57:498-499
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Vetrichevvel et al. recently described a case of linearly arranged fixed drug eruption (FDE) co-existing with non-segmental lesions. [1] I wish to highlight that such linear pattern is not zosteriform/dermatomal as claimed by the Authors, but rather Blashko-linear as clearly evident from its S-shaped fashion (typical of antero-lateral thoracic Blashko lines). Hence, the diagnosis should be redirected towards "superimposed segmental FDE". In fact, according to a recently proposed paradygm, segmental manifestations of acquired polygenic skin disorders, such as drug-induced inflammatory dermatoses, can manifest as either "isolated" (segmental lesions as the sole manifestation of a dermatosis) or "superimposed" (segmental lesions co-existing with non-segmental, otherwise typical manifestations of a dermatosis). [2] Both forms originate from a postzygotic mutational event but do not imply nor exclude any specific type of such mutation (e.g. loss of heterozygosity). [2]

Vetrichevvel et al.'s case adds up to already reported, yet exceptional instances of drug eruptions occurring in a mosaic form, which include, beside FDE, [1],[3],[4],[5] lichenoid dermatitis, [6],[7],[8],[9],[10] spongiotic dermatitis [11],[12],[13],[14] and pigmented purpuric dermatosis [Table 1]. [15],[16] Segmental lesions were distributed along with Blashko lines in all cases. The superimposed segmental pattern was - somehow surprisingly - frequent (33.3% vs. the 66.7% of the isolated segmental one).{Table 1}

Dermatoses due to drugs are a remarkable model to study the interaction between the environment (i.e. drugs) and genotype (i.e. the [immuno] genetic predisposition to develop a cell-mediated hypersensitivity reaction). Although rare, the occurrence of acquired, non-mendelian skin disorders in a segmental (mosaic) fashion represents an experimentum naturae showing that: 1) such disorders depend not only on environmental factors but also on gene defects; 2) among the allegedly pre-disposing postzygotic mutations, at least some are harbored within resident skin cells.


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