Vasculitis (e.g., Henoch-Schönlein purpura, granulomatosis with polyangiitis): This is a likely diagnosis due to the presence of necrotizing lesions, which can be a manifestation of small vessel vasculitis. The condition often presents with skin lesions, but can also affect other organs.

Infectious diseases (e.g., meningococcemia, staphylococcal or streptococcal sepsis): These conditions can cause necrotizing lesions due to bacterial invasion and toxin production. The presence of fever, shock, and disseminated intravascular coagulation may support this diagnosis.
Autoimmune disorders (e.g., lupus, rheumatoid arthritis): Although less common, autoimmune disorders can cause vasculitis and subsequent necrotizing lesions.
Thrombotic thrombocytopenic purpura (TTP) or hemolytic uremic syndrome (HUS): These conditions are characterized by microangiopathic hemolytic anemia, thrombocytopenia, and renal failure, which can lead to necrotizing lesions.

Meningococcemia: This is a life-threatening condition that requires immediate attention. The presence of necrotizing lesions, fever, and shock should prompt consideration of this diagnosis.
Sepsis due to Neisseria gonorrhoeae or other bacteria: Disseminated gonococcal infection can cause necrotizing lesions, and prompt treatment is essential to prevent long-term sequelae.
Cancer (e.g., leukemia, lymphoma): Although rare, certain types of cancer can cause necrotizing lesions, and a delay in diagnosis can have significant consequences.

Ehlers-Danlos syndrome: This genetic disorder can cause fragile skin and blood vessels, leading to necrotizing lesions.
Pseudoxanthoma elasticum: A rare genetic disorder that affects the elastic fibers in the skin, leading to necrotizing lesions and other systemic manifestations.
Calciphylaxis: A rare condition characterized by calcification of small blood vessels, leading to necrotizing lesions, often in patients with end-stage renal disease.