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 Willis1,2 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.

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.”

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.1012 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.