Vascular Rash that Spares the Trunk: Differential Diagnosis
Single Most Likely Diagnosis
- Henoch-Schönlein Purpura (HSP): A form of vasculitis that commonly presents with a purpuric rash, often sparing the trunk, and is typically seen in children. It is also associated with abdominal pain, arthritis, and renal involvement.
Other Likely Diagnoses
- Erythema Multiforme: An immune-mediated condition characterized by target lesions, which can appear as a vascular rash. While it can affect any part of the body, it might spare the trunk in some cases.
- Urticarial Vasculitis: A condition that presents with urticaria-like lesions due to inflammation of the blood vessels. It can mimic a vascular rash and may have a distribution that spares the trunk.
- Insect Bite Reactions: Certain insect bites can cause a vascular-like rash, especially if there is an allergic reaction involved. The distribution would depend on the exposure to the insects.
Do Not Miss Diagnoses
- Meningococcemia: A severe infection caused by Neisseria meningitidis, which can present with a petechial or purpuric rash. Although the rash can be widespread, early stages might spare the trunk. This condition is life-threatening and requires immediate medical attention.
- Rocky Mountain Spotted Fever (RMSF): A tick-borne illness caused by Rickettsia rickettsii, characterized by a rash that typically starts in the extremities and can spare the trunk initially. RMSF is potentially fatal if not treated promptly.
Rare Diagnoses
- Sweet Syndrome: A rare condition characterized by fever, leukocytosis, and tender, erythematous skin lesions that can mimic a vascular rash. It might spare the trunk but is more commonly associated with systemic symptoms.
- Polyarteritis Nodosa (PAN): A systemic vasculitis that can present with skin manifestations, including a vascular rash. While it's rare and can affect any part of the body, the distribution might spare the trunk in some cases.
- Wegener's Granulomatosis (Granulomatosis with Polyangiitis, GPA): A form of vasculitis that affects small- and medium-sized vessels and can present with a variety of symptoms, including skin lesions. The rash can be part of the systemic involvement and might have a varied distribution.