Heterogeneity of antibody specificity in taiwanese patients with polyneuropathy and IgM paraproteinemia

About half of the Caucasian patients with chronic polyneuropathy and IgM pa raproteinemia show serum anti-myelin-associated glycoprotein (MAG) and anti -sulfoglucuronosyl glycosphingolipid (SGGLs) activities. These antibody act ivities have been demonstrated to react with a carbohydrate epitope known a s the HNK-1 or sulfoglucuronic acid (SGA) epitope, However, in Asian popula tions the occurrence of serum anti-SGA activities has been reported to be r elatively rare. We investigated 5 cases of chronic polyneuropathy with IgM paraproteinemia from Taiwan and found that 3 of them had high-titer serum a nti-SGA (SGGL/MAG) antibody activities. The clinical symptoms of these 3 pa tients were consistent with sensory dominant polyneuropathy with a severer involvement of the lower limbs than of the upper limbs. Electromyography an d nerve conduction studies revealed severe sensory nerve involvement (no re sponse in 3 cases) and moderate slowing of motor conduction velocity (MCV) without conduction block. The decrease in MCV correlated well with anti-SGA antibody titer (less than 30 m/s with the titration of 1:12,800, normal 55 -60 m/s), Pathological findings showed active demyelinating polyneuropathy with myelin ovoid and myelinated fiber loss. Our data suggest that anti-SGG L antibody activities may not be very rare among Asian populations. Additio nally, there seems an intriguing possibility that the titer of this antibod y correlates with the severity of peripheral nerve involvement in patients of demyelinating polyneuropathy with IgM paraproteinemia.