What is a neuroma?

Neuroma: Definition and Clinical Implications

A neuroma is a benign enlargement of a nerve that forms as a result of disorganized axonal regeneration following nerve injury, often causing significant pain and functional impairment. 1

Pathophysiology

Neuromas develop through the following mechanism:

• When a peripheral nerve is injured or transected, the proximal nerve stump attempts to regenerate and reconnect with its distal target
• If regenerating axons are impeded from reaching their target, they grow in a disorganized fashion, leading to fascicular escape and scarring 2
• This results in a tangled mass of neural tissue that becomes hypersensitive and painful

The molecular mechanisms involved include:

• Upregulation of neurotrophic factors that stimulate nerve growth
• Neuroinflammatory peptides and cytokines that contribute to pain signaling
• Abnormal expression of transient receptor potential and ionotropic channels 1

Types of Neuromas

1. Traumatic neuromas - Form after nerve injury or transection
2. Morton's neuroma - A specific type affecting the common plantar digital nerve, typically in the third webspace of the foot 3
3. Amputation neuromas - Develop after limb amputation
4. Ganglioneuroblastoma and neuroblastoma - These are distinct entities that represent peripheral neuroblastic tumors arising from the embryonic neural crest 4

Clinical Presentation

Patients with symptomatic neuromas typically experience:

• Burning or shooting pain at the site of nerve injury
• Hypersensitivity to touch (allodynia)
• Electric shock-like sensations with pressure
• Reduced quality of life due to chronic pain 1
• Functional limitations in the affected area

For Morton's neuroma specifically:

• Burning pain in the webspace between toes (usually third)
• Sensation of walking on a pebble
• Pain that worsens with weight-bearing activities 3

Diagnosis

Diagnosis of a neuroma typically involves:

• Clinical history of nerve injury or trauma
• Physical examination revealing a tender, palpable mass along the course of a nerve
• Positive Tinel's sign (tingling sensation when the affected area is tapped)
• Imaging studies such as ultrasound or MRI to visualize the neuroma
• In some cases, diagnostic nerve blocks to confirm the source of pain

Treatment Options

Treatment should be tailored based on the severity of symptoms and impact on quality of life:

Non-surgical Management

• Activity modification to reduce pressure on the affected nerve
• Appropriate footwear or padding for Morton's neuroma
• Oral medications including:
  • Neuropathic pain medications (gabapentin, pregabalin)
  • Anti-inflammatory medications
  • Tricyclic antidepressants

Injection Therapy

For Morton's neuroma:

• Ultrasound-guided corticosteroid with local anesthetic injections are more effective than non-guided injections (moderate-certainty evidence) 3
• Ultrasound guidance improves both pain reduction and functional outcomes

Surgical Interventions

When conservative measures fail:

• Surgical resection of the neuroma
• Implantation of the nerve end into muscle tissue to prevent recurrence
• Capping the nerve stump with epineural graft 5
• For Morton's neuroma, neurectomy through either plantar or dorsal approaches 3

Prevention of Neuroma Formation

To minimize neuroma formation after nerve injury:

• Immediate nerve repair or reconstruction when possible
• Use of laser or scissors rather than electrocoagulation for nerve transection
• Minimizing scar formation during nerve surgery
• Proper handling of nerve tissue during surgical procedures 5

Prognosis and Complications

• Many patients experience persistent pain despite treatment
• Surgical interventions may lead to complications including:
  • Hypertrophic scarring
  • Wound infections
  • Recurrent neuroma formation
  • Sensory deficits in the distribution of the resected nerve 3

Key Considerations

• Early intervention may improve outcomes
• Multidisciplinary approach involving pain specialists, surgeons, and rehabilitation specialists is often necessary
• Patient education about realistic expectations is important, as complete pain resolution is not always achievable
• Novel therapeutic approaches targeting the molecular mechanisms of neuroma formation are under investigation 1