Background: Although neuropathies complicating multiple myeloma (MM) are common as a result of medications and spinal cord compression, neuropathy as a consequence of cross reactivity between the paraprotein and neural tissues is rare. In CANOMAD syndrome (chronic ataxic neuropathy, ophthalmoplegia, M-protein, agglutination, anti-disialosyl antibodies) IgM paraproteins with shared reactivity between Campylocacter jejuni lipopolysaccharides and human peripheral nerve disialylated gangliosides including GQ1b have been described. In POEMS syndrome (polyneuropathy, organomegaly, endocrinopathy, M-protein, and skin changes) cerebral spinal fluid concentrations of vascular endothelial growth factor (VEGF) may be markedly elevated, similar to other inflammatory polyneuropathies. Guillain-Barre syndrome (GBS) is an acute inflammatory demyelinating polyradiculopathy yielding flaccid areflexic paralysis that, to our knowledge, has only been reported once as a complication of MM.Case reports: At Hackensack University Medical Center we have observed 5 cases of GBS complicating MM since 2002 (approximate incidence <0.5%). Details are described below. In all five cases, blood and cerebrospinal fluid cultures, anti-GQb1, anti-GM1, and anti-MAG antibodies were negative and radiographic imaging including computerized axial tomographic scan (CT) of the head and magnetic resonance imaging (MRI) of the brain were unrevealing. In four patients cerebrospinal fluid examination showed albumin/cytologic dissociation.Conclusions: Our observation represents the first series of patients with GBS complicating MM, and suggests that GBS, although rare, should be considered as part of the neurologic complications of plasma cell dyscrasias.CaseAgeSexType of MyelomaMM TherapyPresenting symptoms168MIIIB IgD lambdaVAD, Mel 200 PBSC, month 9, recurringCN VI palsy, areflexia upper extremities, hyporeflexia lower extremities, paresthesias feet & side face263MIIIA IgA kappaDex-Thal, Mel 200 PBSC, week 2Parasthesias hands, legs, and feet. Motor weakness lower extremities ascending.368MIIIA IgG kappaDex-Thal, CDEP, Mel 200 PSCT, wk 3Bilateral facial, sternocleidomastoid, neck muscle weakness with sluggish gag reflex. Upper and lower muscles weak and hyporeflexic.481FIII A IgA kappa + urineDex-LenolidomideLower extremity weakness, with areflexia and severely ataxic gait. Sensory defects in LE.525MIgA lambda plasma-cytomasNone (GBS presenting feature)Marked LE weaknessCSF proteinMotor Nerve ConductionsSensory Nerve ConductionsTreatment & Response1126 mg/dlProlonged median F wave latencyProlonged DSL superficial peronealPlasmapheresis, dex, thalidomide (improved)277 mg/dlSeverely prolonged DML, Reduced CMAP amplitudes, Slow CV, Conduction blockAbsent SNAPsPlasmapheresis (no response), IVIG (improved)376 mg/dlProlonged F wave latencies, Slow CV, Reduced CMAP amplitudesAbsent SNAPsIVIG (minimal response), plasmapheresis (slow improvement)4202 mg/dlProlonged distal motor latencies, Reduced amplitudes of CMAPS in lower extremities, Prolonged F wave latencies, Slow CV in lower extremitiesAbsent or reduced amplitudes of SNAPsIVIG (no response), plamapheresis (improved)559 mg/dlProlonged DML, Prolonged F wave latencies or absent F waves, Mild slowing CV, Mild reduction of CMAP amplitudesNormalIVIG and plasmapheresis (no response, paraplegia), Mel 200 PBSC X2 (improved)