What is the difference between mononeuropathy and radiculopathy?

Distinguishing Mononeuropathy from Radiculopathy

Mononeuropathy affects a single peripheral nerve in its anatomical distribution, while radiculopathy involves dysfunction of a nerve root at the spinal level, following a dermatomal pattern. 1, 2

Anatomical Localization

Radiculopathy:

• Follows a single dermatome distribution pattern originating from the spinal nerve root 2
• Results from dysfunction of a cervical spinal nerve, the roots of the nerve, or both 1
• Commonly caused by compressive pathology at the neural foramina from facet or uncovertebral joint hypertrophy, disc bulging/herniation, or degenerative spondylosis 1

Mononeuropathy:

• Limited to the distribution of one specific peripheral nerve distal to the nerve root 2
• Common examples include carpal tunnel syndrome (median nerve) and peroneal neuropathy at the fibular head 2
• Can be caused by entrapment, compression in anatomically restricted channels, or microvascular occlusion 3

Clinical Presentation Differences

Radiculopathy typically presents with: 1

• Neck pain combined with unilateral arm pain
• Sensory or motor deficits in a dermatomal distribution
• Pain radiating along the nerve root pathway
• Symptoms that may resolve spontaneously or with conservative treatment in most acute cases 1

Mononeuropathy presents with: 2, 4

• Focal symptoms limited to one peripheral nerve territory
• Numbness, paresthesia, or weakness in the specific nerve distribution
• No neck or back pain unless there is concurrent pathology
• Symptoms confined to the anatomical course of the affected nerve 5

Diagnostic Approach to Differentiation

Step 1: Evaluate the sensory examination 5

• Determine if sensory signs follow a peripheral nerve distribution (mononeuropathy) or dermatomal distribution (radiculopathy)
• Look for irritative or negative sensory signs in the specific pattern 5

Step 2: Assess deep tendon reflexes 5

• Differential hyporeflexia can distinguish between the two localizations
• Radiculopathy typically causes reflex loss corresponding to the affected root level 5

Step 3: Identify weak muscle groups 5

• Determine if weakness follows a myotomal pattern (radiculopathy) or peripheral nerve pattern (mononeuropathy)
• This is the most reliable method for precise localization 5

Key Clinical Example

Wrist drop differential: 5

• Radial neuropathy (mononeuropathy): weakness of wrist and finger extensors, sensory loss over dorsal first web space, preserved triceps function
• C7 radiculopathy: weakness may include triceps, wrist extensors, and finger extensors, with sensory loss in C7 dermatomal distribution (middle finger)

Common Pitfalls to Avoid

• Do not rely solely on imaging findings without clinical correlation, as MRI shows high rates of false-positive findings in asymptomatic individuals over age 30 1
• Recognize that entrapment neuropathies can coexist with polyneuropathy or radiculopathy, particularly carpal tunnel syndrome which may precede systemic conditions by years 6
• Avoid assuming symmetric presentation rules out mononeuropathy, as diabetic mononeuropathies can affect cranial nerves or occur as entrapment neuropathies in already damaged nerves 3
• Physical examination findings may not correlate with MRI evidence of nerve root compression in radiculopathy, leading to both false-positive and false-negative imaging results 1

Electrodiagnostic Testing Role

Nerve conduction studies and EMG are essential when clinical examination alone cannot definitively localize the lesion 5, 7

• Provides information on localization and pathophysiology of nerve injury 7
• Not routinely needed for classic presentations with clear clinical localization 6
• Most valuable when atypical features are present, such as acute/subacute onset or asymmetric involvement 7