Monoclonal Gammopathy of Undetermined Significance (MGUS) In Patient With Chronic Urticaria

Introduction: Typically, MGUS is asymptomatic and is an incidental finding when patients undergo protein electrophoresis, which makes the diagnosis of MGUS challenging to make. Due to the lack of symptoms, the diagnosis of MGUS is heavily reliant on labs. Diagnostic criteria is based on four aspects, all of which must be present to make the diagnosis. First, there is no end organ damage present. This means there is a lack of hypercalcemia, renal failure, anemia, and bone lesions. Second, the monoclonal protein must be less than 30 g/L. Third, clonal plasma cells must make up less than 10% of the bone marrow. Fourth is the absence of B-cell lymphoma or other diseases known to produce an M-protein.

According to the literature, the risk of MGUS undergoing malignant transformation into multiple myeloma is 1% each year. Chronic urticaria has been associated with MGUS and other malignancies in patients with Schnitzler syndrome [5] but there have not been any case reports of chronic urticaria due to MGUS in patients without Schnitzler syndrome.

Case Study: We highlight a case of a 75-year-old male with no significant past medical history on whose diagnosis of MGUS was based on the presence of a treatment resistant chronic urticarial rash.
Patient presented with itchy erythematous weals located on his torso, back, shoulders, ankles, and bilateral inner medial thighs for the past seven years. Patient had undergone a trial of antihistamines and Xolair which had him provided him with little to no relief of symptoms. The patient was then test and found negative for H. pylori and ASO titer but was found to have an elevated RF and CRP and a positive ANA. A punch biopsy was then performed and upon serum protein electrophoresis an IgM Lambda M-spike was found. Leukocyte and lymphocyte flow showed decreased B-cells with no findings concerning for malignancy and a PET/CT showed no osseous lesions. Patient was advised that a bone marrow biopsy would needed to have the definitive diagnosis but the patient preferred to monitor labs and defer the biopsy. He was then started on cyclosporine and medrol as needed which he stated provided relief from his symptoms.

Discussion: Clinicians should be aware that cutaneous manifestation that are an unusual presentation and can be observed in MGUS. It is imperative that clinicians consider MGUS with chronic urticaria as a missed diagnosis could have serious health consequences.