Senile Purpura: This is the most likely diagnosis, especially in elderly patients, due to the natural aging process that leads to decreased collagen and elastin in the skin, making it more susceptible to bruising and purpura.

Vasculitis: Conditions like leukocytoclastic vasculitis can cause purpura, especially on the lower legs. This is due to inflammation of the small blood vessels.
Thrombocytopenia: A low platelet count can lead to purpura due to the body's reduced ability to form blood clots.
Coagulopathy: Disorders affecting the blood's ability to clot, such as those caused by medications (e.g., anticoagulants) or diseases (e.g., liver disease), can result in purpura.
Trauma: Physical injury to the lower leg can cause purpura due to blood leakage into the skin.

Meningococcemia: Although rare, this condition is life-threatening and can cause purpura. It's essential to consider this diagnosis, especially in patients with fever, shock, or signs of meningitis.
Disseminated Intravascular Coagulation (DIC): A serious disorder in which the proteins responsible for blood clotting become overactive, leading to the formation of small blood clots in various blood vessels throughout the body. Purpura can be a manifestation.
Sepsis: Infection leading to a systemic inflammatory response syndrome (SIRS) can cause purpura among other symptoms.

Amyloidosis: A condition characterized by the deposition of amyloid (a particular type of protein) in various tissues of the body, which can lead to purpura.
Scurvy: Vitamin C deficiency can cause purpura due to its role in collagen synthesis and blood vessel integrity.
Ehlers-Danlos Syndrome: A group of disorders that affect connective tissues supporting the skin, bones, blood vessels, and many other organs and tissues. Some types can lead to easy bruising and purpura.