Diagnosis aided by distribution
This rash is confined to the V of the neck and extensor exposed surfaces of the arms and upper back and hence is suggestive of a photo induced disorder. An annular, slightly scaly rash like this is seen in subacute lupus erythematosus. To confirm the diagnosis, perform a skin punch biopsy and collect a second specimen for immunofluorescence, as well as checking ANA and ENA antibodies. In subacute lupus, expect to see a positive Ro ENA antibody; it is responsible for the photosensitivity state. Don’t forget to consider medications as a cause. Treat with strict sun protection and hydroxychloroquine if slow to respond.
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