Hypertrophic lichen planus clearly resembles extrusive igneous rock, as nicely shown by Welsh et al.1 But I ask 1 question: What image does the term igneous rock create in the mind of a dermatologist (or a geologist, for that matter)? Unlike the term peau d'orange, for instance, which creates a specific image, the term igneous rock conjures up no specific image. To a dermatologist like myself from New England, igneous rock might suggest granite. But to someone from the West Coast or Hawaii, it probably suggests volcanic rock like rhyolite, basalt, pumice, or obsidian. I'm afraid that the term igneous rock is so vague that it does nothing to facilitate communication.
Reynolds O. Ambiguous Igneous Rocks. Arch Dermatol. 2007;143(1):115-126. doi:10.1001/archderm.143.1.118