Black & blue marks that appear as blotches under the skin may
result from abnormal blood coagulation in patients with active lupus.
Purpura is the term for this phenomenon. If the purpura
is small & feels markedly different from normal skin when touched
without looking, this may be a warning sign of active systemic vasculitis
or low platelet counts (called thrombocytopenic purpura).
An ecchymosis is a spot caused by loss of blood from a vessel, forming an irregular, blue or purplish patch. It has a more diffuse border than purpura.
Black & blue marks that cannot be felt may result
from the use of NSAIDs or steroids.