Seronegative anti-GBM Disease with Coexistent ANCA Positivity.

Anti-glomerular basement membrane disease has been reported to coexist with anti-neutrophil cytoplasmic antibody (ANCA) positive vasculitis. Seronegative anti-GBM disease has been previously described and mostly blamed for the relative insensitivity of earlier serologic assays. A 58-year-old male was transferred to our facility for acute kidney injury. Prior to his hospital admission, the patient had a 2 week history of progressive fatigue, fevers, anorexia, vomiting, decreased urine output, sinus congestion, and non-productive cough. His creatinine reached 13 mg/dL. P-ANCA was positive, anti GBM antibody was negative twice, and urinalysis showed hematuria. Chest x-ray demonstrated diffuse opacities, concerning for pulmonary hemorrhage. Renal biopsy showed a severe necrotizing and crescentic glomerulonephritis with circumferential crescents. There was bright linear glomerular basement membrane staining with IgG consistent with anti-GBM disease. Given these findings, the patient was started on oral cyclophosphamide (160 mg daily), in addition to pulse dose methylprednisolone. He was also initiated on therapeutic plasma exchange. Due to worsening renal function, hemodialysis was started. The patient was discharged from the hospital and completed a course of treatment with cyclophosphamide and prednisone but remains oligo-anuric and hemodialysis dependent at 150 days since presentation. This case highlights the importance of tissue diagnosis in situations similar to this.

Micropthalmia transcription factor (MITF) as a diagnostic marker for metastatic melanomas negative for other melanoma markers.

Metastatic malignant melanoma has a wide spectrum of histopathologic patterns and often lacks melanin pigment. Without a known primary tumor, the diagnosis of metastatic malignant melanoma relies on a combination of morphology and immunohistochemical profile. Infrequently, commonly used markers for melanoma (S100, HMB45, Melan-A and Tyrosinase A) are negative. These cases pose critical diagnostic challenges. Recent studies show that Microphthalmia Transcription Factor (MITF) has high sensitivity (88-100%) and specificity for metastatic melanoma. We are reporting here three cases of high grade tumors that were studied by a comprehensive immunohistochemical panel including cytokeratins, S100, HMB-45, Melan A, Tyrosinase, and MITF. All three tumors were also analyzed for the presence of BRAF mutations. All three metastatic tumors were negative for S100, Melan A, HMB-45 and Tyrosinase but positive for MITF. Subsequent to the diagnoses, previously existing or concurrent primary melanomas were identified in 2 of the 3 cases. Interestingly, S100, Melan A, and HMB-45 were positive in the primary tumors. No BRAF (V600E) mutations were identified in the three metastatic melanomas and CD 117 (c-kit) was positive in one of the cases. In summary, our experience shows that MITF can be a valuable adjunct in the diagnosis of metastatic tumors that are suspicious for melanoma but negative for other melanoma markers.