Diagnosis of Restless Legs Syndrome

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Chapter 15 Diagnosis of Restless Legs Syndrome

Restless legs syndrome (RLS), like most syndromes, represents multiple biological pathologies that share a common clinical presentation. As such, the diagnosis of RLS relies almost entirely on the subjective report of symptoms matching the defining features of RLS. Nonetheless, the nonspecific but sensitive objective motor signs of RLS—periodic limb movements while lying resting awake (PLMW) and while asleep (PLMS)—provide important support for the diagnosis. Given the critical nature of the clinical presentation, after a brief review of the historical development of the diagnosis, this chapter explores the clinical aspects of the defining features. The four clinical features that define RLS appear to be simple enough, but clinicians commonly misunderstand them and fail to appreciate some of their specific expressions. Accurate diagnosis starts with a full understanding of these four defining features as they manifest in RLS. The diagnosis can be further aided by three supportive features of RLS and by recognition of differing RLS phenotypes. This chapter ends with the presentation of tools that have been developed to support making the RLS diagnosis.

History

What appears to be the earliest description of RLS in the medical literature by Willis ^1,² in the 17th century emphasizes both the abnormally excessive movements and their occurrence during usual sleep times. References to RLS after Willis appear to largely assign RLS to a psychiatric or psychological disorder (e.g., related to anxiety³ or, more specifically, financial worries⁴) until the middle of the 20th century, when Ekbom⁵ described the presentation of the disorder in a large series of cases. His work both provides the name currently used for the disorder and establishes RLS as a neurologic disorder. Ekbom emphasized the sensory aspects (paresthesias in the legs) of the disorder⁶ more than the motor features (contractions of the legs) described by Willis. Even after this excellent work, RLS remained largely ignored until the latter part of the 20th century, when a small group of clinicians treating RLS patients formed the International Restless Legs Syndrome Study Group (IRLSSG) and developed the first clinical consensus on the diagnosis of RLS.⁷ These diagnostic criteria restored the emphasis on the movement aspects of RLS and in particular noted an urge to move the legs often but not always associated with the paresthesias. There remained some confusion in the criteria established by this group, particularly in relation to the concept of “restlessness.” These issues were resolved in a National Institutes of Health workshop where the current diagnostic standards were developed.⁸ Thus, as shown in Box 15-1, the RLS diagnosis has evolved from observed movements to the recognition of the akathisia focused in the legs and modulated by diagnostically significant factors.

BOX 15-1 Evolution of Restless Legs Syndrome (RLS) Diagnosis

Willis (1685)	Movement and sleep disruption described
Ekbom (1945)	Sensory disturbance emphasized
American Academy of Sleep Medicine (AASM) (1990)	Sensory and periodic leg movement disturbance of sleep, nocturnal worsening emphasis
International Restless Legs Syndrome Study Group (IRLSSG) (1995)	Restores emphasis on movement as “restlessness”
Restless Legs Syndrome Foundation/IRRLSG/National Institutes of Health Workshop (2002)	Final formulation of diagnostic standards
	Emphasis on “urge to move,” removes motor restlessness and separates effects of rest and activity; clears up some concepts related to supportive features

Essential Diagnostic Criteria

All four of the diagnostic criteria given in Box 15-2 must be met to make the diagnosis of RLS, and failure to meet any one of these excludes the RLS diagnosis. These four criteria appear deceptively simple, but further examination reveals several subtle aspects embedded in these diagnostic features.

Criterion 1: Urge to move the legs usually but not always accompanied by an unpleasant or uncomfortable sensation in the legs. This first essential diagnostic criterion defines the basic symptoms of RLS, which must include a strong urge to move the legs or what is best described as an akathisia focused in the legs. This focal akathisia may occur in either one or both legs and may be focused in only a part of the leg or foot or may extend to include other parts of the body, but it must involve the leg. This is a conscious sensation of an urge to move the leg and not an unconscious habit such as foot tapping when sitting. Movements made without awareness occur with RLS as rather abrupt involuntary physiologic flexors of the legs similar to the periodic leg movements of sleep, but these do not involve a sensation of the urge to move and do not suffice for the diagnosis of RLS. The patient reporting that others note they move a lot or even notice themselves to be moving a lot are not reporting a symptom that meets this criterion. This criterion requires the patient to be fully aware of the urge to move and describes that sensation as localized to or arising from the legs.

The focal akathisia also occurs over a significant duration of time lasting at least a few minutes unless relieved by actions reducing the akathisia, usually moving the legs or other affected body part. The momentary discomfort due to an uncomfortable posture that can be relieved by postural change should not be confused with the need to move of RLS.

The importance of ensuring the presence of this basic aspect of RLS cannot be overemphasized. For example, conditions have been reported that appear to have all the features of RLS without the focal akathisia but with the involuntary leg movements of RLS. These are described as quiescegenic nocturnal dyskinesias and do not show the same clinical pattern as RLS; in particular, they are not universally responsive to dopaminergic treatment.

This diagnostic criterion also includes abnormal and unpleasant sensations in the legs that usually, but not always, accompany the akathisia, but when they occur, they are associated with or even seen as causing the akathisia. These sensations, although decidedly unpleasant, are generally not seen as painful, although in some case series of clinical patients, 30% to as many as 56% report that symptoms are painful.⁹ The type of pain reported, however, is not the severe hurting pain of a leg cramp, for example, but more like an ache such as a toothache. Because these RLS sensations arise without any detectable abnormality in the leg, they have no common intersubjective reference and patients find it very hard to describe these symptoms. They usually say the sensations are like some imagined event, such as worms crawling in the veins. Box 15-3 lists some of the common subjective patient reports of these sensations. Although psychological methods to better define the characteristics of these abnormal sensations exist, they have not yet been used. Nonetheless, the sensations appear to have two basic dimensions. First, they are more dynamic than static; that is, they often involve a sense of something moving through the leg or in the leg and they are not like a point source of pain. Second, they are deep in the leg, often described as in the bone and not on the skin or surface of the leg. Thus, one description is an “itch in the bone.”

BOX 15-2 Essential Restless Legs Syndrome (RLS) Diagnostic Criteria

All four of the following criteria must be met to make the diagnosis of RLS:

1. An urge to move the legs occurs, usually accompanied or caused by uncomfortable and unpleasant sensations in the legs.

2. The urge to move or unpleasant sensations begin or worsen during periods of rest or inactivity, such as lying down or sitting.

3. The urge to move or unpleasant sensations are partially or totally relieved by movement, such as walking or stretching, at least as long as the activity continues.

4. The urge to move or unpleasant sensations are worse in the evening or night than during the day or only occur in the evening or night.

The next three criteria define features that modulate the expression of the RLS symptoms defined by the first criterion. The second diagnostic criterion defines the features that engender RLS, whereas the third criterion defines those that reduce the symptoms and the fourth defines the strong circadian pattern of symptom expression.

Criterion 2: Rest engenders RLS symptoms. Rest here involves two features: decreased movement occurring when sitting or lying down and also decreased mental activity. These provide the conditions that engender RLS symptoms. The suggested immobilization test (SIT) relies on this aspect of RLS (see Chapter 18). In this test, the subject is to stay awake and not move while sitting upright in bed with the legs stretched out in an environment devoid of any changing stimulation. This creates the rest condition provoking the RLS symptoms. The symptoms are expressed by both the occurrence of the urge to move and the periodic limb movements (PLM) representing either involuntary movements or a response to this urge that cannot be suppressed under these conditions. Studies have shown that as the duration of the rest gets longer, the RLS symptoms are more likely to both occur and become more severe. This validates the diagnostic relation between rest and RLS.¹⁰^–¹² Thus, rest acts as a stimulus producing the symptoms that increase in strength with the degree and duration of the rest. It is important to recognize that it is any rest situation that produces the RLS symptoms and not a particular resting body position. Thus, symptoms that occur only with a particular body position such as sitting with the legs crossed are not likely to represent those produced by RLS. Any rest that lasts long enough should engender the symptoms. Because lying down represents a more restful position than sitting, some subjects may report symptoms only when lying down and may not observe them when sitting.

Some subjects with milder RLS may require a longer period of rest before the symptoms are expressed, and if they fall asleep quickly, they may therefore experience their symptoms mostly when sitting for a while and only rarely when lying down. The RLS diagnosis should be questioned whenever the patient reports symptoms only when sitting and hardly ever when lying down unless the symptoms are mild and occur only after a relatively long duration of sitting.

It is generally reported that increased confinement and decreasing general movement enhances the effects of rest. Thus, symptoms are commonly reported to occur when sitting in airplanes, cars, or theaters, even in patients who rarely have the symptoms at other times.

Criterion 3: Leg movements relieve RLS symptoms. The degree of relief appears related to the degree of leg movements. Simply moving the legs while lying down may help some, but more relief is provided by standing and even more by walking. Two features of the relief from movement are often missed. First, the relief should at least be partly felt almost immediately or very soon after the movement is started. The relief occurs because of the movement and not as a result of exercise or intensity of activity. Some patients may have trouble identifying how long it takes for movement to relieve the symptoms, but most, when carefully questioned, recognize the rapid, at least partial relief occurring immediately with or shortly after the onset of the movement. Second, the relief occurs while moving and should persist for as long as the movement continues. The immediacy and persistence of the relief with movement aid in the diagnosis of RLS.

Some patients may confuse relief persisting after movement stops with that during the movement. When asked if symptoms are relieved by movement, they may say something like, “No, the symptoms come back when I stop moving.” But the report of symptoms returning when movement ceases indicates they are less during movement.

It deserves note that movement is only one method to relieve RLS symptoms. Subjects report that any intense conversation or argument, intense mental involvement such as in a computer game, eating, hard rubbing of the legs, and very hot baths also reduce symptoms. As shown in Table 15-1

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