Workup for Allodynia
The workup for allodynia requires establishing the diagnosis through clinical examination with specific sensory testing using standardized tools like Von Frey monofilaments or Semmes-Weinstein monofilaments, identifying the underlying cause (neuropathic pain condition), and assessing functional impact before initiating treatment.
Diagnostic Approach
Step 1: Confirm Allodynia and Establish Neuropathic Pain Diagnosis
- Clinical examination is the cornerstone - allodynia is diagnosed when a patient reports pain in response to normally non-painful stimuli (light touch, gentle pressure, temperature changes) 1
- Use standardized sensory testing tools:
- Von Frey monofilaments or Semmes-Weinstein monofilaments (#5.18, 15g force) to map areas of static mechanical allodynia 2
- The diagnosis should be based on the patient's subjective report (painful vs. not painful), not just fiber type involvement 3
- Allodynography (mapping the cutaneous area of allodynia) has excellent inter-rater reliability (ICC 0.97) and test-retest reliability (ICC 0.89) 2
Step 2: Identify the Underlying Cause
Common conditions causing allodynia include 1:
- Postherpetic neuralgia
- Diabetic neuropathy
- Fibromyalgia
- Complex regional pain syndrome (CRPS)
- Peripheral nerve injuries
- Post-surgical pain syndromes
- Chemotherapy-induced neuropathy
If uncertain about the diagnosis, refer to a pain specialist or neurologist 4
Step 3: Quantitative Sensory Testing (Optional but Informative)
- Current perception threshold (CPT) testing can evaluate sensory nerve function using different frequencies:
- 2,000 Hz (Aβ fibers)
- 250 Hz (Aδ fibers)
- 5 Hz (C fibers)
- In postherpetic neuralgia, the intensity of dynamic allodynia inversely correlates with preserved function across all fiber types 5
- This testing helps differentiate peripheral vs. central mechanisms 5
Step 4: Assess Comorbidities and Functional Impact
Identify relevant comorbidities that affect treatment selection 4:
- Cardiac disease (affects TCA use)
- Renal or hepatic disease (affects dosing)
- Depression (common comorbidity)
- Gait instability
Assess emotional and functional impact 1:
- Pain intensity (numeric rating scale 0-10)
- Quality of life measures
- Functional limitations
- Sleep disturbance
Key Clinical Pitfalls
- Don't confuse allodynia with hyperalgesia: Allodynia = pain from non-noxious stimuli; hyperalgesia = increased pain from normally painful stimuli 3
- Don't delay referral: If the diagnosis is uncertain or if initial management fails, refer to specialists early rather than continuing ineffective treatments 6, 4
- Don't assume allodynia is a contraindication to treatment: Contrary to older beliefs, patients with allodynia respond well to appropriate interventions like spinal cord stimulation 7
Documentation Requirements
- Map the specific area of allodynia using standardized tools
- Document the type of stimulus that provokes pain (touch, pressure, temperature)
- Record pain intensity at baseline for monitoring treatment response
- Note any temporal patterns (constant vs. episodic)
The workup is primarily clinical and does not typically require extensive laboratory or imaging studies unless needed to diagnose the underlying causative condition 8, 1.