Differences Between Polyneuropathy and Multifocal Mononeuropathy
Polyneuropathy is a diffuse, symmetrical, length-dependent disorder affecting multiple peripheral nerves simultaneously, while multifocal mononeuropathy involves damage to individual nerves in multiple locations, presenting with asymmetric, focal deficits in the distribution of specific nerves.
Polyneuropathy
Definition and Presentation
- Polyneuropathy is characterized by diffuse, symmetrical involvement of peripheral nerves, typically beginning distally and progressing proximally in a length-dependent pattern 1
- Symptoms usually begin symmetrically in the toes and feet, later progressing to fingertips as the condition advances 1
- Presents with distal, symmetric sensory or sensorimotor deficits including numbness, paresthesia, pain, and sometimes weakness 1
Clinical Features
- Symptoms are typically bilateral and symmetric, affecting both sides of the body equally 1, 2
- Physical examination reveals distal sensory loss, reduced or absent reflexes, and sometimes distal muscle weakness 1
- Gait may be wide-based and unsteady due to proprioceptive sensory loss 1
- Autonomic symptoms may be present, including orthostatic hypotension, alternating diarrhea and constipation, urinary retention, and sexual dysfunction 1
Diagnostic Testing
- Nerve conduction studies show diffuse abnormalities with relatively uniform involvement of tested nerves 1
- Electromyography typically reveals length-dependent patterns of abnormalities 1
- Small-fiber polyneuropathy may have normal conventional nerve conduction studies and requires skin biopsy to detect decreased epidermal nerve fiber density 3
Multifocal Mononeuropathy
Definition and Presentation
- Multifocal mononeuropathy (also called mononeuropathy multiplex) involves damage to individual nerves at multiple locations 1, 4
- Presents as asymmetric, focal deficits in the distribution of specific nerves 5, 4
- Can affect sensory, motor, or both sensory and motor functions of the involved nerves 5, 6
Clinical Features
- Symptoms follow the distribution of individual peripheral nerves 7, 4
- Deficits are typically asymmetric, affecting different nerves on different sides of the body 6, 4
- May initially mimic isolated mononeuropathies but eventually reveals a pattern of multiple nerve involvement 5
- Can affect cranial nerves, causing focal deficits like facial weakness or visual disturbances 1
Diagnostic Testing
- Nerve conduction studies show focal abnormalities with conduction block or slowing limited to specific segments of individual nerves 7, 6
- Electromyography reveals denervation limited to muscles innervated by specific affected nerves 7
- MRI may show nerve root enhancement or thickening in some cases 1
Key Differences
Distribution Pattern
- Polyneuropathy: Symmetric, distal, length-dependent pattern affecting all nerves simultaneously 1, 2
- Multifocal mononeuropathy: Asymmetric, patchy distribution affecting individual nerves in multiple locations 5, 4
Progression
- Polyneuropathy: Typically progresses gradually from distal to proximal in a symmetric fashion 1
- Multifocal mononeuropathy: May progress with stepwise involvement of different nerves at different times 4
Etiology
- Polyneuropathy: Often associated with metabolic disorders (diabetes), toxic exposures, nutritional deficiencies, or hereditary conditions 2
- Multifocal mononeuropathy: Frequently associated with vasculitis, immune-mediated processes, diabetes, compression, or infiltrative diseases 4
Electrodiagnostic Findings
- Polyneuropathy: Diffuse abnormalities affecting all nerves in a length-dependent pattern 1
- Multifocal mononeuropathy: Focal abnormalities with conduction blocks or slowing limited to specific segments of individual nerves 7, 6
Clinical Implications
- The distinction between these two conditions is crucial as they often have different underlying causes requiring different treatment approaches 1, 5
- Multifocal mononeuropathy may have significant therapeutic implications as it often results from treatable inflammatory or vasculitic processes 4
- Polyneuropathy management typically focuses on treating the underlying cause and symptom management, while multifocal mononeuropathy may require immunosuppressive therapy if caused by inflammatory processes 1