From the Guidelines
The most appropriate test to obtain next is a serum protein electrophoresis (option E). This 59-year-old man presents with concerning symptoms including back pain, fatigue, weight loss, and laboratory findings of hypercalcemia, renal insufficiency, and anemia. These findings, along with the L4 compression fracture, strongly suggest multiple myeloma. Serum protein electrophoresis would help identify the presence of monoclonal proteins (M-proteins), which are characteristic of multiple myeloma, as stated in the guidelines by 1. This test is essential for diagnosis before proceeding with more invasive testing like bone marrow biopsy.
The patient's symptoms and laboratory results meet the CRAB criteria for multiple myeloma, which includes hypercalcemia (calcium level of 11.8 mg/dL), renal insufficiency (creatinine level of 2.20 mg/dL), anemia (hematocrit of 32%), and bone lesions (L4 compression fracture) 1. The guidelines also recommend evaluating bone marrow plasma cell infiltration and lytic bone lesions, but serum protein electrophoresis is a crucial initial step in the diagnosis of multiple myeloma.
While a CT scan of the chest might be reasonable given his smoking history, the constellation of hypercalcemia, renal failure, anemia, and bone lesion (CRAB features) makes multiple myeloma the more pressing diagnosis to investigate. Parathyroid hormone level would be useful for primary hyperparathyroidism, but the clinical picture is more consistent with malignancy, as suggested by the guidelines 1. Prostate-specific antigen is less relevant given the specific laboratory abnormalities present.
Key points to consider in this diagnosis include:
- The presence of monoclonal proteins (M-proteins) in serum or urine, which is a hallmark of multiple myeloma 1
- The evaluation of bone marrow plasma cell infiltration, which can be done through bone marrow aspiration and/or biopsies 1
- The assessment of lytic bone lesions, which can be done through radiological skeletal bone survey, MRI, or CT scan 1
- The presence of end-organ damage, such as hypercalcemia, renal insufficiency, anemia, and bone lesions, which is a key criterion for the diagnosis of multiple myeloma 1
From the Research
Diagnostic Approach
The patient presents with a 1-month history of increasing low back pain, fatigue, and weight loss, which are common symptoms of multiple myeloma. The laboratory results show elevated calcium levels, renal impairment, and anemia, which are also consistent with multiple myeloma.
Relevant Tests
The following tests are relevant in this scenario:
- Serum protein electrophoresis (SPEP) to detect and quantify monoclonal gammopathy, which is a hallmark of multiple myeloma 2, 3, 4
- Bone marrow biopsy to confirm the diagnosis of multiple myeloma and to assess the extent of disease 2, 5
- Imaging studies, such as CT scan, to evaluate the extent of bone disease and to detect any lytic lesions
Most Appropriate Test
Based on the patient's symptoms and laboratory results, the most appropriate test to obtain next would be:
- E. serum protein electrophoresis (SPEP) to detect and quantify monoclonal gammopathy, which is a key diagnostic criterion for multiple myeloma 2, 3, 4
Rationale
SPEP is a sensitive and specific test for detecting monoclonal gammopathy, which is a hallmark of multiple myeloma. The test can help differentiate multiple myeloma from other conditions, such as monoclonal gammopathy of undetermined significance (MGUS) and polyclonal gammopathies 3. Additionally, SPEP can be used to monitor disease response and progression in patients with multiple myeloma 5.