Differential Diagnosis

• Single most likely diagnosis
  • Granulomatosis with polyangiitis (GPA): This diagnosis is most likely due to the presence of c-ANCA positivity, which is a hallmark of GPA. The patient's symptoms, including haematuria, sinusitis, and crescents on renal biopsy, are also consistent with GPA.
• Other Likely diagnoses
  • Microscopic polyangiitis (MPA): Although less likely than GPA due to the absence of p-ANCA and the presence of c-ANCA, MPA can still present with similar symptoms and renal findings.
  • Eosinophilic granulomatosis with polyangiitis (EGPA): This diagnosis is possible, especially if the patient has a history of asthma or eosinophilia, but it is less likely due to the lack of specific mention of these features.
• Do Not Miss
  • Goodpasture’s disease: Although anti-GBM antibodies are negative, it is crucial to consider this diagnosis due to the potential for severe renal and pulmonary involvement. A negative serology does not entirely rule out Goodpasture’s disease, especially if there is a high clinical suspicion.
• Rare diagnoses
  • Idiopathic crescentic glomerulonephritis: This is a rare condition characterized by the presence of crescents on renal biopsy without an identifiable cause. It is less likely given the patient's systemic symptoms but should be considered if other diagnoses are ruled out.
  • ANCA-associated vasculitis with atypical features: There are rare instances where ANCA-associated vasculitis presents with atypical features or overlapping syndromes, making diagnosis challenging. A thorough evaluation and follow-up are necessary to refine the diagnosis.