Sensory Preservation in Carpal Tunnel Syndrome vs. Pronator Teres Syndrome
In carpal tunnel syndrome (CTS), sensation in the palm is typically NOT preserved, while in pronator teres syndrome (PTS), palmar sensation is typically preserved due to the anatomical differences in nerve compression locations. 1
Anatomical Basis for Sensory Differences
Carpal Tunnel Syndrome
- Compression occurs at the wrist level, affecting the main median nerve trunk after the palmar cutaneous branch has already branched off
- Presents with prominent palmar sensory loss in the median nerve distribution (radial 3½ digits)
- Nocturnal paresthesias are common and characteristic
- Symptoms are exacerbated by wrist flexion or extension
- Positive Tinel's and Phalen's signs at the wrist 1
Pronator Teres Syndrome
- Compression occurs more proximally in the forearm
- Palmar cutaneous nerve function is typically preserved
- Presents with forearm pain exacerbated by repetitive pronation
- Less consistent palmar sensory deficits compared to CTS
- Symptoms provoked by resisted pronation or elbow flexion
- Nocturnal paresthesias are typically absent (an important distinguishing feature) 1, 2
Diagnostic Considerations
Key Differentiating Features
- If paresthesia involves the thenar eminence and proximal forearm pain is noted in a case of suspected CTS, consider concurrent CTS and PTS 3
- The palmar cutaneous branch of the median nerve (PCBm) is not affected in isolated CTS but may be affected in PTS 4
- In a study of patients with CTS, 56% had abnormal PCBm conduction, suggesting potential concurrent compression or anatomical variations 5
Diagnostic Challenges
- The two conditions can coexist (double crush syndrome), complicating the clinical picture
- Among cases of CTS, approximately 6% may have concurrent pronator syndrome 3
- Standard nerve conduction studies are highly sensitive for CTS but may miss proximal median nerve compressions like PTS 1
Clinical Pearls and Pitfalls
Common Pitfalls
- PTS is often misdiagnosed as CTS due to symptom overlap
- Failure to recognize concurrent compression syndromes can lead to incomplete treatment response
- Relying solely on electrodiagnostic studies without thorough clinical examination may lead to missed diagnoses 2, 6
Diagnostic Approach
- Ultrasound is highly sensitive and specific for CTS diagnosis, showing enlargement and flattening of the median nerve 1, 7
- MRI can identify median nerve abnormalities in both conditions with high accuracy 7
- Consider PCBm sensory conduction studies to help differentiate between the conditions 4
- Always evaluate for both conditions when median nerve compression is suspected 2
By understanding these key differences in sensory preservation patterns, clinicians can more accurately distinguish between CTS and PTS, leading to more appropriate treatment decisions.