Can hypogammaglobulinemia cause a false negative DIF in bullous disease?   

Patient has had longstanding pancytopenia, CVID on IVIG.  Now with bullous disease involving oral mucosa, back, extremities... repeated biopsy of oral mucosa and skin lesions nonspecific ulceration.  Bone marrow biopsy unrevealing.  Multiple pan scans and endoscopies show no evidence of neoplasm.  Topical oral and systemic steroids help but disease flares after tapering.    Could DIF be a false negative in hypogammaglobulinemia?