AL amyloidosis is not present as an incidental finding in cutaneous biopsies of patients with multiple myeloma

Summary Multiple myeloma (MM) is a monoclonal B‐cell neoplasm characterized by autonomous proliferation of immunoglobulin‐secreting plasma cells that are capable of synthesizing amyloidogenic light chains resulting in AL amyloidosis. Clinically occult AL amyloid deposition may occur in up to 31% of patients with MM. The prognosis of combined amyloidosis and MM is improving with new therapeutic options. Thus it is imperative that patients with MM be screened for amyloidosis. Sixty‐six consecutive skin biopsies from patients with MM and the diagnosis of graft vs. host disease (GVHD) were stained with Congo red and assessed for the presence of amyloid deposition. Twelve cases that had amyloid deposition in other tissue and had a cutaneous biopsy were also stained with Congo red and assessed for the presence of amyloid deposition. None of the 66 biopsies of GVHD, and none of the 12 cases that had documented amyloid deposition in other tissue showed evidence of amyloid deposition in the cutaneous biopsies. In the absence of specific cutaneous manifestations of amyloidosis, it is unlikely that amyloidogenic light chain deposition in the skin would be found. Type I collagen may appear similar to amyloid, both by light microscopy and fluorescence, after staining with Congo red. Thus care must be taken not to confuse type I collagen autofluorescence with positivity for amyloid when assessing skin biopsies stained with Congo red.