Differential Diagnosis

• Single most likely diagnosis
  • Granulomatosis with Polyangiitis (GPA): This diagnosis is most likely due to the combination of symptoms such as sinus congestion, headaches, fatigue, weight loss, and palpable purpura, along with the positive c-ANCA result. c-ANCA is a specific type of autoantibody often associated with GPA, which is a form of vasculitis affecting small- and medium-sized vessels.
• Other Likely diagnoses
  • Microscopic Polyangiitis (MPA): Although less likely than GPA given the c-ANCA positivity, MPA is another form of vasculitis that could present with similar symptoms, including weight loss, fatigue, and purpura. However, MPA is more commonly associated with p-ANCA.
  • Eosinophilic Granulomatosis with Polyangiitis (EGPA): This condition, formerly known as Churg-Strauss syndrome, is characterized by asthma, eosinophilia, and vasculitis. While it could be considered, the absence of asthma or eosinophilia in the provided history makes it less likely.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Infections (e.g., Endocarditis, Osteomyelitis): Given the patient's recurrent sinusitis and current fever, it's crucial to rule out infections that could mimic or complicate vasculitis. Endocarditis, for example, can cause systemic symptoms and embolic phenomena that might resemble vasculitis.
  • Malignancy: Weight loss and recurrent infections could also suggest an underlying malignancy, which would require prompt investigation and treatment.
• Rare diagnoses
  • Polyarteritis Nodosa (PAN): This is a medium-vessel vasculitis that can present with systemic symptoms, including weight loss and fatigue. However, it is not typically associated with ANCA positivity and is less common than the other vasculitides mentioned.
  • Relapsing Polychondritis: This condition involves inflammation of cartilaginous structures and can present with a variety of symptoms, including those affecting the respiratory tract. However, it would be an unusual diagnosis given the combination of findings in this patient.