Short description: The term whiplash as such includes both the mechanism of a trauma and a collection of symptoms found after exposure to a certain type of injury (8,59). Immediate exposure to a whiplash-type neck distortion is consistent with the S13.4 diagnosis, which is a nonspecific neck distortion diagnosis. The chronic whiplash syndrome S13.4C is described by a collection of symptoms and plausible exposure to a whiplashlike injury of the neck.

In the IHS International Classification of Headache Disorders (ICHD)-II, a distinction is made between acute headache attributed to whiplash injury (ICHD-II code 5.3) and chronic headache attributed to whiplash injury (ICHD-II code 5.4) (see Table 107-1).

Whiplash injury is produced when acceleration and deceleration forces act on the neck, resulting in hyperextension, hyperflexion, and, occasionally, hyperrotation of the cervical spine. Rear-end or side-impact car collisions (39) or other types of events can cause whiplash injury (58).

The Quebec Task Force (58) proposed the whiplash-associated disorder (WAD) criteria to grade the severity of a whiplash injury (Table 107-1). The criteria resemble previous classifications (43) and have been widely adopted. The term chronic WAD, defined as persisting WAD symptoms after 6 months postinjury, is acknowledged, and it is essentially identical with the widely used terms chronic whiplash syndrome and late whiplash syndrome.

A Canadian epidemiologic survey indicated that the incidence of compensated whiplash was 0.70 per 1000 inhabitants per year in 1987 (0.85 per 1000 women and 0.54 per 1000 men) in Quebec and 10 times higher in Saskatchewan (58). Notably, Saskatchewan changed from the tort system to the no-fault system in 1995 (14), resulting in a reduced number of insurance claims and a significant decline in the incidence of long-term pain and disability: a 43% reduction of claims in men and a 15% reduction in women during a 1-year period. This result was contrasted by an increase in the number of vehicle damage claims and number of kilometers driven. A Swedish study reported an incidence of one cervical strain injury per 1000 inhabitants per year (7). At present, the prevalence of whiplash injury is unknown.

In some Western countries, but not in other, the incidence of whiplash injury has increased remarkably during the last decades (5). A 25-year Dutch retrospective study documented a 12-fold increase between 1970 and 1994 in the occurrence of neck sprain after motor vehicle accidents in persons immediately treated and diagnosed at the unit (63). The frequency of neck sprains was highest (0.28 per 1000) among 25- to 29-year-old people. A 1.3-fold increase in number of cars and a 1.7-fold increase in number of kilometers driven were among the proposed explanations for the rise in frequency of neck sprains (63). Also, there was a fourfold increase in neck sprains after noncar accidents: 25% accidental falls, 24% sport traumas, 14% bicycle accidents, and 8% motorcycle accidents during the observation period. Noncar accidents were most frequently reported in young persons (15 to 19 years old: 39 per 100,000; 10 to 14 years old: 34 per 100,000). The increase in neck sprains after noncar accidents was explained by an increase in sport and leisure activities and by mandatory participation in school gymnastics. The largest increase was observed in concert with intensive focusing on whiplash in the media.

A British study found a remarkable increase in road traffic accidents in the years 1982-1991, and the proportion of accidents associated with a diagnosis of neck sprain increased correspondingly (7). For example, 8% of 929 traffic injury victims sustained a neck sprain in 1982-1983 as compared to 46% of 6149 victims in 1991-1992 (7).

IHS ICHD-II diagnostic criteria are as follows:

5.3 Acute headache attributed to whiplash injury

A. Headache, no typical characteristics known, fulfilling criteria C and D.

B. History of whiplash (sudden and significant acceleration/deceleration movement of neck) associated at the time with neck pain.

C. Headache develops within 7 days after whiplash injury.

D. One of the other of the following:

1. Headache resolves within the following 3 months after whiplash injury.

2. Headache persists, but 3 months have not yet passed since whiplash injury.

5.4 Chronic headache attributed to whiplash injury

A. Headache, no typical characteristics known, fulfilling criteria C and D.

B. History of whiplash (sudden and significant acceleration/deceleration movement of neck) associated at the time with neck pain.

C. Headache develops within 7 days after whiplash injury.

D. Headache persists for >3 months after whiplash injury.

Principal symptoms: Neck pain, restricted neck movement/neck stiffness, and headache are the most commonly reported symptoms after acute whiplash injury. High initial pain intensity (56) and initial restriction of cervical mobility (32,50) are related to bad outcome after whiplash injury.

Other more inconsistently reported symptoms are shoulder-arm pain; numbness in the shoulder, arm, and hand; dysphagia and globulus; dizziness; and visual and auditory disturbances (26,30,47,60).

Headache occurs in 40 to over 80% of acute whiplash patients (16). In one study, 34% of all responders reported persistent troublesome neck pain within the last year, and 14% suffered neck pain for more than 6 months (12). A lifetime history of headache is associated with moderate or severe whiplash headache (15,26,33).

Proposed causes of headache in acute whiplash injury are zygapophyseal arthropathy at the cervical C2-C3 level (64), segmental spreading (31), central (36) sensitization of nociceptors giving rise to chronic pain condition, or dysfunction in brainstem or upper cervical medulla (34).