Steroid Purpura — SCE Dermatology MCQ

Correct answer: C — Corticosteroid-induced dermal atrophy and capillary fragility

The correct answer is C, corticosteroid-induced dermal atrophy and capillary fragility. Long-term systemic (or potent topical) corticosteroid use suppresses fibroblast activity and reduces collagen and elastin synthesis in the dermis, causing thinning of the supporting connective tissue around dermal vessels. Without this collagen scaffold, small vessels lose mechanical support and rupture with trivial trauma or even spontaneously, producing purpura and ecchymoses typically over the extensor forearms and hands. Crucially, this purpura occurs with normal platelet count and normal coagulation, distinguishing it as a mechanical/structural vessel problem rather than a haemostatic disorder. This is a well-recognised, dose- and duration-related adverse effect of corticosteroid therapy. Why the other options are wrong: B. Vitamin K deficiency: this causes a coagulopathy (prolonged prothrombin time) from reduced synthesis of clotting factors II, VII, IX and X, which the stem explicitly excludes; it does not cause isolated dermal fragility. D. Vasculitis: this produces palpable purpura from vessel wall inflammation, often with systemic features (arthralgia, renal or gut involvement) and typically affects dependent areas; there is no history here of an inflammatory process, and steroids would usually improve rather than cause vasculitic purpura. E. Scurvy: vitamin C deficiency impairs collagen cross-linking causing perifollicular haemorrhage and gum bleeding, but this is unrelated to corticosteroid exposure and there is no dietary history suggesting deficiency. A. Platelet dysfunction: this would usually show abnormal bleeding time or be associated with thrombocytopenia or antiplatelet drugs, both excluded by the stem stating no thrombocytopenia or coagulopathy. Key point: Non-thrombocytopenic, non-coagulopathic purpura on thinned, atrophic skin in a patient on long-term steroids reflects loss of dermal collagen support causing capillary fragility, not a clotting or platelet defect.

Reference: BNF (NICE), Prednisolone: side-effects and cautions of corticosteroids, including skin thinning and easy bruising; https://bnf.nice.org.uk/drugs/prednisolone/