Improvement of pure sensory mononeuritis multiplex and IgG1 deficiency with sitagliptin plus Vitamin D3

Introduction: Mononeuritis multiplex (MM) is an unusual form of peripheral neuropathy involving at least two noncontiguous peripheral nerve trunks. The pure sensory form of MM occurs rarely. Immunoglobulin (Ig)G subclass deficiency is a clinically and genetically heterogeneous disorder. Up to 50% of adults with selective subnormal IgG1 levels or selective IgG1 deficiency have a concomitant autoimmune disorder. Herein, we report the case of a patient with MM and selective IgG1 deficiency who showed remarkable clinical improvement after 2-year combination therapy with the DPP-4 inhibitor sitagliptin plus vitamin D3.Case report: A 49-year-old man developed numbness in right hand and forearm. After 6 months, the patient developed left forefoot numbness. Approximately 8 years later, the patient started to develop numbness also in the right forefoot, along with symptoms of evening fatigue and occasional orthostatic hypotension. The patient also reported recurrent candidiasis in glans and intergluteal areas since adolescence. Electromyoneurography of lower and upper limbs revealed the presence of multiple mononeuropathies. Protein electrophoresis showed hypogammaglobulinemia and low serum IgG1 levels. Sural nerve biopsy showed the presence of perineuritis. The patient was diagnosed with MM due to perineuritis probably secondary to IgG1 deficiency. We, then, proposed combination therapy with sitagliptin and vitamin D3 in the attempt to achieve immunomodulation. At the last follow-up visit (2 years), the patient showed persistent clinical improvement, increase in IgG1 levels and normalization of protein electrophoresis.Conclusions: To the best of our knowledge, this is the first case showing a remarkable clinical improvement of MM and selective IgG1 deficiency achieved through a combination therapy with sitagliptin and vitamin D3.