Differential Diagnosis for Svc Distribution Rash

• Single most likely diagnosis
  • Herpes Zoster (Shingles): This is the most likely diagnosis due to the characteristic dermatomal distribution of the rash, which is often seen in the distribution of the superior vena cava (Svc) area, such as the thoracic or trigeminal dermatomes.
• Other Likely diagnoses
  • Contact Dermatitis: This could be a possible diagnosis if the patient has come into contact with an allergen or irritant that has caused a reaction in the Svc distribution area.
  • Eczema (Atopic Dermatitis): Eczema can present with a rash in various distributions, including the Svc area, especially if the patient has a history of atopic diseases.
  • Psoriasis: Although less common, psoriasis can have a wide range of presentations, including a rash in the Svc distribution.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Varicella-Zoster Virus infection in an immunocompromised patient: Although Herpes Zoster is already considered, the context of an immunocompromised patient elevates the urgency due to the risk of disseminated zoster.
  • Lyme Disease: Early stages of Lyme disease can present with a rash (erythema migrans), which, although typically singular, could be confused with other rashes. Missing this diagnosis could lead to serious complications if not treated promptly.
• Rare diagnoses
  • Svc syndrome due to a malignancy or thrombosis: While extremely rare to present as a rash, superior vena cava syndrome can cause skin manifestations due to the obstruction of blood flow, which could potentially be confused with a dermatomal rash.
  • Neurosyphilis: In its tertiary stage, syphilis can cause a wide range of neurological and dermatological symptoms, including rashes that might mimic those seen in the Svc distribution, although this would be quite rare and usually accompanied by other symptoms.