A 60-year-old woman with a medical history of atrial tachycardia managed with diltiazem and required electrical cardioversion three years ago, and a diagnosis of IgM monoclonal gammopathy of undetermined significance (MGUS) one year prior, presented with two weeks of worsening occipital headaches and blurry vision. Her headache, initially intermittent, intensified in the last 72 hours, and she developed blurred vision the night before the presentation. She denied fevers, night sweats, nausea, vomiting, chest pain, shortness of breath, cough, appetite changes, weight loss, or easy bruising. In the emergency department, her vital signs were normal. Physical examination revealed tender occipital and cervical lymphadenopathy, mild splenomegaly, and bilateral retinal hemorrhage. Magnetic Resonance Imaging (MRI) findings revealed normal cervical spine and brain scans.

Laboratory results showed a WBC of 5.17 K/μL, Hgb of 9.0 g/dL, MCV of 87.8 fL, platelet count of 462 K/μL, IgG of 639 mg/dL, IgA of 53 mg/dL, IgM of 6,810 mg/dL, and serum viscosity of 5.0 centipoises. These results indicate a significant increase in IgM levels, which is a characteristic of the patient's condition. She received intravenous fluids and acetaminophen with minimal improvement in headache and worsening vision, indicating complications related to IgM MGUS, including hyperviscosity syndrome, requiring further management.