Essential tremor: The role of biobehavioral conditioning.

Abstract

Abstract Essential Tremor [ET], the most common neurological movement disorder, has been described as a purely medical condition, with little consideration of how principles of behavior may come to exert joint control over tremor, related negative emotional arousal, and verbal behavior. A biobehavioral conditioning model is described that has been useful in accounting for these behaviors and in developing biobehavioral interventions. ********** Essential tremor (ET) is the most prevalent neurological movement disorder with approximately 14% of the population being affected by the disorder (Koller, Busenbark, Miner et al., 1994). ET is dominantly inherited with variable penetrance (Rautakorpi, Martilla, & Rinne, 1984). In such cases it is referred to as familial essential tremor. The term idiopathic essential tremor is used to classify the significant number of individuals who develop ET absent a family history of the disorder. Men and women are equally affected. Peak incidence occurs in the seventh (20.3%) decade of life (Koller et al., 1994). Hispanic and African American individuals are at greater risk of developing the disorder than other ethnic groups (Louis, Marder, Cote, et al., 1995). ET can be distinguished from Parkinson's disease based on several characteristics. For example, among individuals with Parkinson's disease cogwheel rigidity or ratcheting, observed when an upper limb is extended and flexed, bradykinesia (slowness of movement) and imbalance when ambulating are used as soft neurological signs to discriminate ET from Parkinson's disease (Elble & Koller, 1990). Finally, ET is pathologically distinct from Parkinson's disease, which is caused by a loss of dopaminergic cells in the substantia nigra. While various causal biological mechanisms have been imputed, the pathophysiology of ET appears to be linked to the thalamus (Tasker, 1998). ET most often affects the hands and head; however, tremor of the lower limbs may also occur over time (Koller et al, 1994). Tremor involves continuous or intermittent oscillation resulting in horizontal, vertical and/or rotational movement (Lundervold, 1997). Tremor may also be defined according to three types of situations (Elble & Koller, 1990). Resting tremor occurs when the limbs are fully supported, as is the case when one is sitting in an armchair. Kinetic tremor occurs during the act of movement, such as reaching for an object. Postural tremor occurs when a posture is sustained against gravity, such as holding one's arms outstretched. Individuals afflicted by ET are often significantly disabled in communication, work, emotional adjustment, home management, and leisure activities (Bain, Findley, Atchinson, Behari, et al., 1993; Busenbark, Nash, Nash, Hubble, & Koller, 1991; Koller, Biary, & Cone, 1986; Koller et al., 1994). Approximately 50% of the individuals with ET have disability in performance of activities of daily living (ADL) involving use of the hands (Auff, Doppelbauer, & Fertl, 1991; Bain et al., 1993). Approximately 20% of individuals with ET report having such significant disability that they must leave their jobs or reduce their job responsibilities due to motor or anxiety-related disability (Metzer, 1992; Rautakorpi et al., 1984). Numerous clinical observations clearly point to the development of fear and avoidance behavior, such as social phobia secondary to tremor-related physical disability (Lundervold, 1997; Metzer, 1992; Wake et al., 1974). The primary forms of intervention for ET are neurosurgery and medication. Neurosurgery may take two forms: severation of nerves of the brain thought to be responsible for the tremor or implantation of electrodes used in brain stimulation (Andrew, 1981; Tasker, 1998). Brain surgery is highly intrusive, expensive, and experimental limiting its application. Pharmacological treatment using Primidone, an antiseizure medication, or beta-blockers, such as Inderal, is not entirely satisfactory. …