Pre-Existing Conditions: What You Need to Know

Based on 96 WSIAT decisions mentioning pre-existing conditions

The Myth: “I Had Pain Before, So I Can’t Claim”

WRONG! You can still win a WSIB claim even with pre-existing conditions.

What the Law Actually Says

Under Ontario’s WSIA (Workplace Safety and Insurance Act):

  • Work doesn’t need to be the sole cause of your disability
  • Work just needs to contribute significantly
  • Pre-existing conditions don’t disqualify you

Three Ways to Win With Pre-Existing Conditions

1. Aggravation

Work made your existing condition worse

Example from cases:

  • Had mild back pain for years (manageable)
  • Workplace lifting injury made it severe (can’t work)
  • WSIB is responsible for the worsening

2. Acceleration

Work sped up an inevitable decline

Example from cases:

  • Had degenerative disc disease (common aging)
  • Would have worsened slowly over 10-20 years
  • Work accident caused immediate severe degeneration
  • WSIB covers the accelerated timeline

3. Distinct New Injury

Work caused a different injury than pre-existing

Example from cases:

  • Pre-existing: Left knee arthritis
  • Work injury: Right knee torn meniscus
  • Clearly separate injuries

How WSIB Uses Pre-Existing Conditions Against You

Common arguments from 96 analyzed cases:

“This is just natural progression”

  • WSIB claims your condition would have worsened anyway
  • Counter: Show sudden change after specific work event

“You had the same symptoms before”

  • WSIB points to old medical records showing similar complaints
  • Counter: Document increased severity or new limitations

“Independent medical exam says pre-existing”

  • WSIB-paid doctor attributes disability to pre-existing condition
  • Counter: Get your own medical opinion explaining work contribution

Medical Evidence Strategy

What Your Doctor Should Document

✅ Baseline function before work injury

  • “Patient could work 8-hour shifts with occasional back discomfort”

✅ Specific work event that changed things

  • “On March 15, patient lifted 50lb box, felt immediate severe pain”

✅ Post-injury deterioration

  • “Now unable to stand >30 minutes, requiring narcotic pain medication daily”

✅ Work contribution statement

  • “In my medical opinion, workplace injury aggravated pre-existing condition, rendering patient unable to work in current job”

Diagnostic Evidence

  • Imaging before vs. after work injury (if available)
  • Functional capacity testing showing current limitations
  • Treatment escalation (more aggressive treatment needed after work event)

Types of Pre-Existing Conditions in Claims

From case analysis:

Pre-Existing Condition Frequency Can Still Win?
Degenerative disc disease Common ✅ Yes (if work aggravated)
Arthritis Common ✅ Yes (if work worsened symptoms)
Previous injury (same area) Moderate ⚠️ Harder (need clear distinction)
Chronic pain Moderate ⚠️ Harder (must show worsening)
Mental health conditions Less common ✅ Yes (if work trauma distinct)

The “Thin Skull” Rule

Legal principle working in your favor:

“Take your victim as you find them”

  • If you’re more vulnerable due to pre-existing condition, that’s not your fault
  • Work should have accommodated your limitations
  • If they didn’t, and you got hurt, they’re still liable

Common Mistakes to Avoid

❌ Hiding your medical history

  • WSIB will find it anyway
  • Looks like you’re being dishonest
  • Instead: Be upfront, explain how work made it worse

❌ Not getting treatment history

  • You need records showing baseline condition
  • Request all medical records from past doctors

❌ Accepting WSIB’s IME opinion without challenge

  • You have the right to your own independent medical exam
  • Get a second opinion from a doctor you choose

Appeal Strategy

Building Your Case

  1. Timeline: Create detailed timeline showing:
    • Pre-injury status (what you could do)
    • Specific work incident
    • Post-injury decline (what you can’t do now)
  2. Medical evidence: Get letters from:
    • Treating physician (knows your history)
    • Specialist (expert opinion on causation)
    • Functional evaluator (objective testing)
  3. Work evidence: Gather:
    • Job description (what duties were required)
    • Incident reports (documenting specific event)
    • Employer accommodation attempts (or lack thereof)

At the Hearing

WSIAT looks for:

  • Credibility: Consistent story across all reports
  • Medical opinion: Doctor clearly states work contribution
  • Temporal connection: Symptoms worsened right after work event
  • Causation explanation: Medical reason WHY work made it worse

Real Case Pattern Examples

Pattern 1: “Existing Condition + Workplace Accident”

  • Worker had mild scoliosis (spinal curvature) since childhood
  • Workplace fall caused herniated disc
  • Outcome: WSIB responsible for disc injury and worsening scoliosis symptoms

Pattern 2: “Degenerative Disease + Occupational Aggravation”

  • Worker had early-stage arthritis (common for age 50+)
  • Years of repetitive lifting accelerated degeneration
  • Outcome: WSIB responsible for occupational disease component

Pattern 3: “Previous Injury + New Distinct Trauma”

  • Worker recovered from 2019 back strain
  • 2024 workplace accident caused new disc herniation different level
  • Outcome: WSIB responsible for new injury

Thunder Bay Resources

  • Community Legal Assistance Thunder Bay (CLATB)
  • WSIB appeals specialists
  • Office of the Worker Adviser (free provincial service)

Medical Evidence

  • Request complete medical file from all providers
  • Consider private physiatry assessment if WSIB IME unfavorable
  • Thunder Bay Regional HSC has specialists familiar with WSIB cases

Ready to Appeal?

📝 Pre-Existing Condition Appeal Template - Fill-in-the-blank WSIAT appeal letter specifically for pre-existing condition denials (96 decisions analyzed). Takes 45-60 minutes to complete. Addresses the “take your victim as you find them” principle.

Bottom Line

Having a pre-existing condition does NOT disqualify you from WSIB benefits.

You must prove:

  1. Work made it worse (aggravation)
  2. Work sped it up (acceleration)
  3. Work caused a new injury (distinct)

Get strong medical evidence explaining the work contribution.

Data source: 96 cases mentioning pre-existing conditions from 1,334 WSIAT decisions