Amyloid‐Like Immunoglobulin Deposition Neuropathy

BACKGROUND AND AIMS: Amyloid-like immunoglobulin deposition neuropathy is a rare cause of polyneuropathy, characterised by unique clinical and histological features in combination with proteomics that distinguish it from both amyloidosis and anti-MAG neuropathy. While light microscopic findings resemble amyloidosis with 'amyloid-like deposits', they are negative for Congo-red stain and have granular ultrastructure appearances under electron microscopy, unlike the characteristic fibrillary appearance of amyloid. METHODS: We present five cases of polyneuropathy associated with IgM paraprotein, without anti-MAG antibodies, with a distinctive phenotype: predominant neuropathic pain, skin changes or neuropathic ulcers, and a progressive distal sensory neuropathy. RESULTS: All patients demonstrated an axonal sensorimotor neuropathy and histopathology of 'amyloid-like' (Congo-red negative) material with predominant granular deposition on electron microscopy consistent with a combination of heavy and light chain deposition. Skin involvement demonstrated similar histological features, but there was no evidence of renal or cardiac involvement. Most patients had treatment for their underlying haematological disorder and subsequently had no further progression in their neuropathy. DISCUSSION: Amyloid-like immunoglobulin deposition neuropathy is a slowly progressive painful axonal polyneuropathy associated with paraproteinaemia. Diagnosis is made with biopsy and electron microscopy. Treatment targets the source of the paraproteins and controls disease progression, leading to favourable survival compared to AL amyloidosis.