What are the diagnostic criteria and treatment options for prurigo nodularis?

Prurigo Nodularis: Diagnosis and Management

Prurigo nodularis (PN) is diagnosed by the presence of firm, nodular lesions, pruritus lasting at least 6 weeks, and evidence of repeated scratching, picking, or rubbing. The diagnosis requires careful exclusion of underlying systemic conditions that may trigger or exacerbate the condition 1.

Diagnostic Criteria

Clinical Features

• Essential diagnostic findings:
  • Multiple firm, hyperkeratotic nodules (typically 0.5-3 cm)
  • Distribution on extensor surfaces of limbs and trunk
  • Intense pruritus lasting at least 6 weeks
  • Evidence of chronic scratching/picking
  • Excoriations and lichenification

Diagnostic Workup

1. Detailed history:

   • Duration and intensity of pruritus
   • Exacerbating factors
   • Previous treatments and responses
   • Associated systemic symptoms

2. Physical examination:

   • Document number, size, and distribution of nodules
   • Look for excoriations, prurigo nodularis-like lesions 2
   • Assess for signs of underlying conditions

3. Laboratory investigations:

   • Complete blood count with differential (eosinophilia)
   • Liver function tests
   • Renal function tests
   • Ferritin levels (iron deficiency) 2
   • Consider specific tests based on clinical suspicion:
     • HIV serology
     • Hepatitis panel
     • Thyroid function tests if clinically indicated

4. Histopathology:

   • Skin biopsy showing:
     • Hyperkeratosis
     • Acanthosis
     • Dermal fibrosis
     • Increased number of dermal nerves

Management Approach

First-Line Treatments

1. Topical therapies:

   • High-potency topical corticosteroids under occlusion
   • Topical calcineurin inhibitors
   • Capsaicin cream 3

2. Intralesional therapies:

   • Triamcinolone acetonide (5-10 mg/mL) for localized lesions

Second-Line Treatments

1. Phototherapy:

   • Narrowband UVB or PUVA therapy
   • Good partial response rates in multiple studies 4

2. Systemic therapies based on severity:

   • Antipruritic agents:

     • Gabapentinoids (pregabalin)
     • Antidepressants (amitriptyline, paroxetine) 4

   • Immunomodulators:

     • Cyclosporine (for severe, refractory cases)
     • Methotrexate
     • Thalidomide (caution: peripheral neuropathy risk) 4

Treatment Selection Algorithm

1. Mild disease (few nodules, limited distribution):

   • Start with topical therapies and intralesional steroids
   • Consider phototherapy if inadequate response after 4-6 weeks

2. Moderate-to-severe disease (numerous nodules, widespread):

   • Combine topical therapies with systemic antipruritic agents
   • Add phototherapy if available
   • Consider immunomodulators for refractory cases

3. Refractory disease:

   • Consider combination therapy with multiple systemic agents
   • Evaluate for undiagnosed underlying conditions

Special Considerations

Comorbidity Management

• Screen for and address associated conditions:
  • Atopic dermatitis
  • Diabetes
  • Thyroid disease
  • Kidney disease
  • Chronic liver disease
  • HIV infection 5

Monitoring and Follow-up

• Assess treatment response using:
  • Reduction in nodule count
  • Decrease in pruritus intensity
  • Improvement in quality of life
  • Follow up every 4-6 weeks initially, then every 3 months

Common Pitfalls to Avoid

1. Misdiagnosis:

   • Failing to distinguish from other pruritic conditions
   • Not performing adequate workup for underlying causes

2. Treatment errors:

   • Using only topical treatments for severe disease
   • Discontinuing treatments prematurely before adequate trial
   • Overlooking psychological impact of chronic pruritus

3. Monitoring failures:

   • Not assessing for treatment-related adverse effects
   • Failing to adjust therapy based on response

PN represents a challenging chronic condition with significant impact on quality of life. Early diagnosis and a structured treatment approach targeting both neural and immunologic components of pruritus are essential for effective management 1, 6.