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From time to time, we come across linear skin lesions. This can be very helpful diagnostically as there is a limited range of possible diagnoses. A careful history and examination of the morphology of the lesions usually sorts them out.
For each of the nine cases, study the image(s) and then answer the questions. You can click on the image to view a larger version if required.
Each case should take approximately 2 minutes to complete. There is a list of suggested further reading material at the end of the quiz.
Name these linear skin lesions.
Koebnerised psoriasis
What is the cause?
A more chronic linear plaque may be puzzling. The main two diagnoses to consider are psoriasis and lichen planus. These are both prone to koebnerise, or arise at the site of skin injury. The injury can be quite minor, often a superficial scratch. Both conditions present as well demarcated infiltrated plaques. But psoriasis tends to be a brighter red colour, and scale can be readily brushed off (as in this case). Lichen planus is known for its violaceous hue, and has adherent scale (Wickham’s striae). It feels a little firmer to palpate, and is more likely to have a polygonal or bizarre shape. Examine the rest of the patient to make a confident diagnosis; sometimes a biopsy is necessary.