What test can confirm the underlying condition predisposing a 59-year-old man with pneumococcal pneumonia and hypercalcemia to infections, given his impaired renal function and current medication of amlodipine (calcium channel blocker)?

Bone Marrow Biopsy is the Test to Confirm Multiple Myeloma in a Patient with Pneumococcal Pneumonia and Hypercalcemia

The bone marrow biopsy (option A) is the most appropriate test to confirm the underlying condition predisposing this patient to pneumococcal pneumonia.

Clinical Presentation Analysis

This 59-year-old man presents with several key findings that strongly suggest multiple myeloma as the underlying condition:

• Pneumococcal pneumonia (confirmed by sputum culture)
• Hypercalcemia (12.3 mg/dL)
• Elevated total protein (9 g/dL) with normal albumin (3.1 g/dL), suggesting paraproteinemia
• Renal impairment (creatinine 2.8 mg/dL)

Why Multiple Myeloma is the Likely Diagnosis

Multiple myeloma is strongly associated with increased susceptibility to encapsulated bacterial infections, particularly Streptococcus pneumoniae 1. The risk for pneumococcal infection is high in persons with decreased responsiveness to polysaccharide antigens, which occurs in multiple myeloma 2.

The constellation of findings in this patient represents the classic tetrad of multiple myeloma:

1. Hypercalcemia
2. Renal dysfunction
3. Anemia (implied by the clinical presentation)
4. Paraproteinemia (suggested by elevated total protein with normal albumin)

Diagnostic Test Selection

Bone Marrow Biopsy (Option A)

• Definitive test: Bone marrow biopsy is the gold standard for diagnosing multiple myeloma, which would reveal plasma cell infiltration
• Multiple myeloma patients typically have >10% clonal plasma cells in the bone marrow
• This test would directly confirm the underlying immunodeficiency predisposing to pneumococcal infection

Why Other Options Are Less Appropriate:

CT of chest, abdomen, and pelvis with contrast (Option B)

• While CT may detect lytic bone lesions associated with multiple myeloma, it is not the definitive diagnostic test
• CT is more appropriate for staging after diagnosis or evaluating complications
• The American College of Radiology recommends CT chest for recurrent pneumonia to identify anatomical abnormalities 3, but this doesn't address the underlying immunologic disorder

HIV antibody (Option C)

• While HIV can predispose to pneumococcal infections, the patient's laboratory findings (hypercalcemia, elevated total protein, renal impairment) are more consistent with multiple myeloma
• HIV typically doesn't cause hypercalcemia as a primary manifestation

Sweat chloride testing (Option D)

• This tests for cystic fibrosis, which can predispose to respiratory infections
• However, cystic fibrosis typically presents earlier in life and doesn't explain the hypercalcemia or elevated total protein

Videoscopic swallow study (Option E)

• This evaluates for aspiration, which can cause recurrent pneumonia
• However, aspiration doesn't explain the hypercalcemia, elevated total protein, or renal impairment

Supporting Evidence

Case reports document pneumococcal infections as the initial presentation of multiple myeloma:

• Pneumococcal bacteremia has been reported as the first sign of multiple myeloma in previously asymptomatic patients 1
• Common features in these cases include S. pneumoniae infection, mild anemia, and indirect evidence of paraproteinemia (increased total protein with low albumin) 1
• Even young patients with pneumococcal infections and hypercalcemia have been diagnosed with multiple myeloma 4

Clinical Approach to Pneumonia with Hypercalcemia

When encountering a patient with pneumococcal pneumonia and hypercalcemia:

1. Consider underlying immunodeficiency conditions, particularly multiple myeloma
2. Evaluate for the classic tetrad of multiple myeloma (hypercalcemia, renal dysfunction, anemia, protein abnormalities)
3. Perform bone marrow biopsy to confirm the diagnosis
4. Initiate appropriate antimicrobial therapy for the pneumonia while simultaneously addressing the underlying condition

Conclusion

The bone marrow biopsy is the most appropriate test to confirm multiple myeloma, which is the most likely underlying condition predisposing this patient to pneumococcal pneumonia based on the constellation of hypercalcemia, renal impairment, and protein abnormalities.