Hello and welcome to HCM, Bruising without a prior history of trauma is suggestive of disorder associated with coagulation or clotting factors. Thus, I suggest you to get some baseline investigations for the coagulation system which include- platelet count, bleeding time, clotting time, prothrombin time (PT) and activated partial thromboplastin time (aPTT). In case of any abnormality of coagulation system, these tests will be abnormal. Another possibility is connective tissue disorder called dermatomyositis characterized by a purple rash on the knuckles area. However, this disorder is also accompanied by pain in muscle area. A clinical examination is required to rule out this possibility. Thus, I suggest you to get above mentioned investigations and also to consult your physician. Thanks and take care Dr Shailja Puri