Giant Cell Arteritis (GCA): This condition is a large vessel vasculitis that can present with jaw pain, fatigue, and purpuric skin lesions, particularly in older adults. The combination of these symptoms, especially the jaw pain, makes GCA a strong consideration.

Henoch-Schönlein Purpura (HSP): A small vessel vasculitis that can cause purpuric skin lesions, often accompanied by joint pain, gastrointestinal symptoms, and sometimes renal involvement. While it's more common in children, it can occur in adults.
Wegener's Granulomatosis (Granulomatosis with Polyangiitis, GPA): A form of vasculitis that affects small- and medium-sized vessels and can present with a wide range of symptoms including skin lesions, jaw pain due to involvement of the facial vessels, and systemic symptoms like fatigue.
Polyarteritis Nodosa (PAN): A medium vessel vasculitis that can cause a variety of symptoms including skin lesions, joint pain, and systemic symptoms. While jaw pain is less commonly highlighted, the condition's systemic nature and potential for skin involvement make it a consideration.

Meningococcemia: A severe infection caused by Neisseria meningitidis, which can present with purpuric skin lesions, fever, and systemic symptoms. It's critical to identify and treat promptly due to its high mortality rate.
Disseminated Intravascular Coagulation (DIC): A condition characterized by both widespread clotting and bleeding in the vascular system, which can lead to purpuric lesions among other symptoms. It often occurs in the context of severe illness or infection.
Thrombotic Thrombocytopenic Purpura (TTP): A rare blood disorder characterized by the formation of blood clots in small blood vessels throughout the body, which can lead to purpura, fatigue, and other systemic symptoms.

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 poor wound healing, which might be mistaken for purpuric lesions.
Pseudoxanthoma Elasticum (PXE): A rare genetic disorder that can cause skin lesions and other systemic symptoms due to the accumulation of mineralized and fragmented elastic fibers in some tissues.
Amyloidosis: A condition characterized by the deposition of amyloid (a particular type of protein) in various tissues of the body, which can lead to a wide range of symptoms including skin lesions and systemic symptoms like fatigue.