Carpal Tunnel Syndrome and Ulnar-Sided Swelling
No, carpal tunnel syndrome does not typically cause swelling on the ulnar side of the hand—CTS affects the median nerve distribution (thumb, index, middle, and radial half of the ring finger), not the ulnar side.
Anatomic Distribution of Carpal Tunnel Syndrome
- CTS causes symptoms in the median nerve distribution, which includes the palmar aspect of the thumb, index and middle fingers, and radial half of the ring finger—not the ulnar side 1
- The classic presentation involves pain and paresthesias limited to median nerve territory 1
- Imaging findings in CTS include enlargement and flattening of the median nerve, bowing of the flexor retinaculum, and increased median nerve cross-sectional area (≥10 mm² at the carpal tunnel inlet) 2, 3
Important Exception: Ulnar Nerve Involvement Without Ulnar-Sided "Swelling"
While CTS does not cause ulnar-sided swelling, there is an interesting phenomenon where the ulnar nerve itself can be affected:
- 34% of patients with CTS demonstrate abnormalities in ulnar nerve function on sensory testing 4
- The ulnar nerve cross-sectional area is significantly enlarged in patients with CTS (5.16 ± 1.04 mm²) compared to controls (3.56 ± 0.52 mm²) on ultrasound 5
- After carpal tunnel release, the ulnar nerve cross-sectional area decreases significantly, suggesting that increased carpal tunnel pressure affects the ulnar nerve even though it does not traverse the carpal tunnel 5
- 53% of CTS patients report paresthesias or numbness in ulnar nerve distribution, and 89% of these symptoms improve after median nerve decompression alone without Guyon's canal release 4
Clinical Pitfall to Avoid
Do not confuse ulnar nerve enlargement (detected on imaging) with visible or palpable ulnar-sided swelling of the hand. The ulnar nerve changes are microscopic findings on ultrasound, not clinically apparent swelling that a patient would notice or that would be visible on examination 5. The mechanism appears to be increased pressure within the carpal tunnel affecting adjacent structures, with the cross-sectional areas of the median and ulnar nerves being significantly correlated 5.
When to Consider Alternative Diagnoses
If a patient presents with actual ulnar-sided hand swelling:
- Consider ulnar nerve entrapment at Guyon's canal rather than CTS 4
- Evaluate for acute carpal tunnel syndrome from fractures, hemorrhagic conditions, or vascular disorders, which may cause more diffuse swelling 6
- Consider systemic conditions if bilateral symptoms are present, as bilateral CTS may indicate amyloidosis or other systemic disease 2, 7