An Alert for Motor Neuron Diseases and Peripheral Neuropathy: Monoclonal Paraproteinemia May Be Missed by Routine Electrophoresis

To the Editor.  —We write to alert neurologists about a problem in laboratory diagnosis. Monoclonal paraproteinemia, or monoclonal gammopathy, a form of plasma cell dyscrasia, seems to be found with inordinate frequency in patients with peripheral neuropathy^1-3 and motor neuron diseases, including amyotrophic lateral sclerosis.⁴ The condition is defined by the identification of a monoclonal immunoglobulin in the serum (M protein).In the United States, electrophoresis on cellulose acetate is commonly used to separate the serum proteins, which are then stained. The gel isQuantitative Analysis of Immunoglobulins Diagnosis IgG, mg/dL (g/L) IgA, mg/dL (g/L) IgM, mg/dL (g/L) Immunofixation Electrophoresis Paraprotein Normal range 700-1700 (7.00-12.00) 70-350 (0.70-3.50) 50-300 (0.50-3.00) Motor neuron disease 652 (6.52) 82 (0.82) 518 (5.18) IgMΚ Neuropathy 1120 (11.20) 285 (2.85) 155 (1.55) IgA λ Motor neuron disease 1050 (10.50) 361 (3.61) 107 (1.07) IgAΚ scanned with a densitometer and the curves are inspected visually;