Management of Left Bicep Pain with Leukocytosis in a 54-Year-Old Female
This patient requires immediate evaluation for bacterial soft tissue infection, specifically pyomyositis or deep cellulitis of the biceps muscle, with urgent imaging and empiric broad-spectrum antibiotics if infection is confirmed.
Immediate Diagnostic Assessment
The laboratory findings are concerning for bacterial infection. A WBC count of 11.2 × 10⁹/L with neutrophils of 8.4 × 10⁹/L (75% neutrophilia) does not meet the threshold for definitive leukocytosis (≥14,000 cells/mm³), but the elevated absolute neutrophil count warrants careful assessment for bacterial infection 1.
Critical Laboratory Evaluation Required
- Obtain a manual differential count immediately to assess for left shift (band neutrophils ≥16% or absolute band count ≥1,500 cells/mm³), as this has a likelihood ratio of 4.7 to 14.5 for bacterial infection even with a borderline total WBC count 1, 2, 3
- Do not rely on automated differential alone—manual assessment is essential for detecting immature neutrophil forms 1, 3
- Measure C-reactive protein (CRP) and procalcitonin if available, as CRP >50 mg/L has 98.5% sensitivity for sepsis 1
- Obtain blood cultures before initiating antibiotics if systemic signs are present 1, 4
Focused Physical Examination
Examine the left bicep specifically for:
- Warmth, erythema, swelling, or fluctuance suggesting abscess or cellulitis 1
- Severe pain out of proportion to examination findings, which may indicate pyomyositis or necrotizing infection 1
- Fever, tachycardia, hypotension, or altered mental status indicating sepsis 2
- Skin breaks, trauma sites, or injection sites that could serve as portals of entry 1
Imaging and Source Identification
Obtain urgent MRI or ultrasound of the left upper extremity to evaluate for:
- Deep soft tissue abscess requiring drainage 1, 2
- Pyomyositis (muscle infection) 5
- Necrotizing fasciitis (surgical emergency) 1
If imaging reveals an abscess, immediate incision and drainage is mandatory with culture of purulent material 1, 2. Cultures should be obtained before antibiotic initiation whenever feasible 1, 4.
Empiric Antibiotic Therapy
If Severe Infection or Systemic Signs Present
Initiate broad-spectrum antibiotics within 1 hour covering both MRSA and streptococci 1, 2:
- Vancomycin 15-20 mg/kg IV every 8-12 hours PLUS piperacillin-tazobactam 3.375-4.5 g IV every 6 hours 1
- Alternative: Vancomycin plus imipenem/meropenem 500 mg-1 g IV every 6-8 hours 1
If Mild-Moderate Cellulitis Without Systemic Signs
For non-purulent cellulitis, coverage against streptococci is essential 1:
- Cefazolin 1 g IV every 8 hours 1
- Consider adding MRSA coverage (vancomycin or linezolid 600 mg PO/IV twice daily) if risk factors present: injection drug use, known MRSA colonization, or penetrating trauma 1
Duration of Therapy
Treat for minimum 5 days, extending therapy if infection has not improved 1. Severe infections may require 7-10 days or longer depending on clinical response 1.
Critical Pitfalls to Avoid
- Do not dismiss infection based on WBC count alone—neutrophilia with left shift can indicate serious bacterial infection even when total WBC is <14,000 cells/mm³ 1, 2, 3
- Do not delay antibiotics if sepsis criteria are met (hypotension, tachycardia, altered mental status)—mortality increases with each hour of delay 2
- Do not assume simple muscle strain—localized pain with leukocytosis and neutrophilia requires exclusion of pyomyositis, which can progress rapidly in immunocompromised or diabetic patients 5
- Do not treat empirically without imaging if abscess is suspected—source control through drainage is essential and antibiotics alone are insufficient 1, 2
- Do not overlook non-infectious causes of neutrophilia in this age group, including stress response, medications, or underlying malignancy, but infection must be excluded first 6