A 52-year-old man with community-acquired pneumonia is started on levofloxacin. After 5 days of therapy, he develops severe tendon pain in the Achilles tendon region with palpable swelling. What is the most appropriate investigation to confirm the suspected fluoroquinolone-induced adverse effect?

Explanation

## Investigation of Fluoroquinolone-Induced Tendinopathy ### Clinical Presentation Fluoroquinolones, particularly older agents like ciprofloxacin and newer ones like levofloxacin, are known to cause tendinopathy—most commonly affecting the Achilles tendon. The patient's presentation of acute tendon pain with swelling after fluoroquinolone initiation is classic. ### Why Ultrasound Is the Investigation of Choice **Key Point:** Ultrasound is the first-line imaging modality for suspected fluoroquinolone-induced tendinopathy because it is: - Non-invasive and readily available - Real-time assessment of tendon structure and echogenicity - Can detect hypoechoic areas, tendon thickening, and partial/complete tears - Cost-effective and no radiation exposure - Allows dynamic assessment (pain with dorsiflexion) ### Diagnostic Features on Ultrasound | Finding | Significance | |---------|-------------| | Hypoechoic or anechoic areas | Tendon edema or micro-tears | | Increased tendon thickness | Inflammatory response | | Loss of normal fibrillar pattern | Structural disruption | | Partial or complete tear | Severity assessment | **High-Yield:** Ultrasound can differentiate between simple tendinitis (edema without tear) and tendon rupture, which guides management (conservative vs. surgical). ### Mechanism of Fluoroquinolone Tendinopathy 1. Inhibition of topoisomerase II in tenocytes 2. Impaired collagen cross-linking and matrix synthesis 3. Increased oxidative stress and apoptosis 4. Weakening of tendon mechanical properties **Clinical Pearl:** Risk factors include age >60 years, concurrent corticosteroid use, renal impairment, and previous tendon disorders—all present in this case. ### When MRI May Be Considered MRI is reserved for: - Inconclusive ultrasound findings - Suspected complex tears or retraction - Pre-operative planning if surgery is contemplated - However, it is NOT the first-line investigation due to cost and time **Warning:** Do not delay diagnosis with advanced imaging—clinical suspicion + ultrasound is sufficient to confirm and guide cessation of the offending drug.