A Rare Etiology of Chronic Polyradiculoneuropathy: IgD Multiple Myeloma

Introduction: Immunoglobulin D multiple myeloma (IgD MM) is a rare entity of multiple myeloma (2%), characterised by its clinical severity, renal presentation and poor prognosis. IgD myeloma remains an exceptional cause of chronic polyradiculoneuropathy. Observation: A 54-year-old patient, known to have type 2 diabetes since 2016, was admitted in December 2020 for non-febrile obnubilation associated with tetraparesis. The interrogation noted the occurrence of a motor deficit of the four limbs for 4 months in connection with a sensitivemotor polyradiculoneuropathy of the axon-myelin type of the four limbs. Glasgow’s score was 10. Blood pressure was 130/80 mmHg, pulse 116 beats/min, temperature 37°C, SaO2 92% on room air, low capillary blood glucose 1.08 and oliguria 70 cc/H. The physical examination revealed meningeal syndrome, tetraparesis, anaemia and renal oedema. Investigations revealed severe hypercalcaemia (140 mg/L), purulent meningitis (purulent liquid CSF, 12.38 g/L protein, 0.52 g/L glycorrhaphy, 14/mm³ leucocytes, 2000/mm³ red blood cells) and acute renal failure (74 mg/L creatinine, 5 mL/min/m³ GFR, 2.65 mg/L urea). Symptomatic IgD multiple myeloma was suspected on the basis of bone marrow plasmacytosis, bilateral frontal diploid lacunar osteolysis on CT scan and IgD positivity. Conclusion: Our observation illustrates the possible plurality of symptoms of IgD MM, particularly chronic polyradiculoneuropathy which is a rare neurological sign that should not be ignored in order to avoid diagnostic errors.