DELAYED ONSET

Summary: Faulty causal attribution is common among physicians and litigators. With the exception of damage to nervous tissue, pain caused by physical injury generally starts within hours. The physiological changes that generate acute pain are complete within days at most. However, vulnerability to re-injury and secondary damage may be compensable.

Causation may be questioned if there is materially delayed onset of symptoms following injury,

Though the claimant reports de novo onset of symptoms immediately or shortly after an accident, review of the contemporaneous medical records may show this to be an error of recall bias. As we have noted elsewhere, attending physicians and claimant independent medical examiners commonly attribute causation purely on the basis of patient's recall, without reviewing the contemporaneous medical records.

Even if record review confirms the timing of onset of symptoms, the post hoc ergo propter hoc fallacy may apply. Attributing a first occurrence of Multiple Sclerosis to a Motor Vehicle Accident is an example of this error.

Where examination of at least 5 years of pre-injury records show that the symptoms are a recurrence of a pre-existing pattern, Damages may be considerably limited or even subject to denial. Relapse of Fibromyalgia Syndrome is a common example.

Practice Point

Questionable Causation:

Recall Bias
Post hoc ergo propter hoc
Recurrence of pre-existing pattern

With the exception of damage to nervous tissue, pain caused by physical injury generally starts within hours. Even when these tests are passed, and the diagnosed medical condition is recognised to be a possible consequence of that injury, undue delay in onset of symptoms should raise doubts about Causation.

It is useful to distinguish between Immediate pain (minutes), Acute pain (hours, days) and Chronic pain (weeks, months^)1. In a survey of 138 patients attending an emergency clinic, rather more that one-third reported not feeling pain at the time of the injury; the majority developed pain within one hour, though for a few it took up to 9 hours or more².

Whereas Immediate and Acute pain can progress to Chronic pain, a useful rule-of-thumb is that pain that occurs de novo weeks or months after an injury was not Caused by that injury. Notable exceptions are nerve, or neuropathic, pain and injury to the spinal cord; that is, the scarring of injured nervous tissue may take weeks or months to develop.

Practice Point

With notable exceptions, local pain that occurs de novo weeks or months after an injury was not Caused by that injury

The physiological changes that generate acute pain are complete within days at most. One of the accepted tests of medical causation is biological plausibility. While it must be acknowledged that our areas of medical knowledge are like oases in a desert of ignorance, many conditions and symptoms that follow Personal Injury defy causal attribution on physiological grounds.

Medical science is just beginning to identify and describe the patho-physiological evolution of Chronic Pain, but this sequence occurs in the presence of pre-existing acute pain. With few exceptions, local Chronic Pain does not develop following innocuous injury.

According to current understanding³, injury and acute inflammation trigger a cascade of physiological changes that take place within minutes, hours and days. These inflammatory changes include a local sensitisation of the nerves such that pain signals are amplified and stimulation that would normally be innocuous or low intensity are now experienced as painful (tenderness, for example^{)4,[Full

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In general, it is biologically implausible that molecular changes that result in acutely painful conditions could occur weeks, months or years after the initiating event.

Practice Point

If s/he proposes causation of de novo onset of acute pain more than hours after injury, ask the medical expert to explain the proposed biological mechanism

However, vulnerability to re-injury and secondary damage may be compensable. In addition to neuropathic causes, pain remote from the site of injury can develop de novo because of altered mechanics. Thus, changes in posture to protect an injured or weakened body part may cause secondary injury. Muscular weakness following immobilisation of a fractured leg may result in a secondary injury that would not otherwise have occurred (Thin Skull).

Similarly, an initial compensable injury may be painless, and local pain develop only when a subsequent uninsured injury, perhaps relatively trivial, occurs to the weakened part. A common example is dislocated shoulder, which stretches the ligaments and predisposes 1to recurrent dislocation with relatively little force.