What is the workup for ulnar (ulnar nerve) neuropathy?

Workup for Ulnar Neuropathy

The diagnostic workup for ulnar neuropathy should include electrodiagnostic studies (nerve conduction studies and EMG) and ultrasound as first-line tests, with MRI reserved for complex cases or when surgical intervention is being considered. 1

Initial Clinical Assessment

• History focus points:

  • Location and character of symptoms (numbness/paresthesia in 4th and 5th digits)
  • Pain in the proximal medial aspect of the elbow
  • Weakness in hand intrinsic muscles
  • Aggravating factors (elbow flexion, prolonged positioning)
  • Risk factors: diabetes, peripheral vascular disease, alcohol dependency, arthritis 1

• Physical examination:

  • Test for sensory deficits in ulnar nerve distribution
  • Assess strength of hand intrinsics, flexor carpi ulnaris, and flexor digitorum profundus
  • Perform elbow flexion test (Tinel's sign at the cubital tunnel)
  • Look for muscle atrophy, clawing of 4th and 5th digits
  • Check for subluxation of the ulnar nerve with elbow flexion

Diagnostic Testing

First-line Tests:

1. Electrodiagnostic studies:

   • Nerve conduction studies (NCS) to measure:
     • Compound muscle action potential (CMAP) amplitude
     • Motor nerve conduction velocity across the elbow
     • Sensory nerve action potentials
   • Electromyography (EMG) to assess denervation in ulnar-innervated muscles 1

2. Ultrasound evaluation:

   • Use high-frequency transducers (10 MHz or more)
   • Measure cross-sectional area/nerve thickness
   • Perform dynamic assessment to detect nerve subluxation
   • Position: patient seated with hand on thigh or examination table
   • Views: transverse volar and longitudinal dorsal scans 1

Second-line Tests:

1. MRI (when indicated):

   • T2-weighted MR neurography to assess for:
     • Nerve signal intensity changes
     • Nerve enlargement
     • Anatomical variants or space-occupying lesions
   • Considered the reference standard for complex cases 1

2. Laboratory testing (to rule out other causes):

   • HbA1c, vitamin B12, folate, TSH
   • Serum protein electrophoresis and immunofixation
   • Consider autoimmune screening: ANA, ESR, CRP 2

Differential Diagnosis Considerations

• Cervical radiculopathy (C8-T1)
• Thoracic outlet syndrome
• Brachial plexopathy
• Peripheral polyneuropathy
• Vitamin B12 deficiency
• Hypothyroidism
• Alcohol toxicity 1

Localization of Ulnar Neuropathy

It's critical to distinguish between:

1. Entrapment under the humeroulnar aponeurosis (cubital tunnel)
2. Compression in the retrocondylar groove
3. Ulnar neuropathy at the wrist (Guyon's canal)
4. Ulnar neuropathy at the forearm 3, 4

Proper localization is essential as it guides treatment decisions, with different approaches needed for different sites of compression.

Pitfalls and Caveats

• Ulnar neuropathy is the second most common entrapment neuropathy after carpal tunnel syndrome 4
• Electrodiagnostic studies have moderate sensitivity but may be limited in precise localization
• Ultrasound can provide better anatomical localization than electrodiagnostic studies alone
• Many cases of mild-moderate ulnar neuropathy may improve spontaneously 4
• Avoid misdiagnosing all ulnar neuropathies as "cubital tunnel syndrome" when the pathology may be elsewhere

The combination of clinical assessment, electrodiagnostic studies, and imaging provides the most comprehensive approach to diagnosing ulnar neuropathy and determining the appropriate treatment strategy.