Insomnia Diagnosis and Differential Diagnosis

Diagnosis and Differential Diagnosis
Unlike the specific sleep disorders already discussed, a sleep recording in the sleep clinic is usually not warranted for complaints of insomnia because insomnia may not occur every night and often patients experience insomnia in their own bed but not in new environments.

As multiple factors may contribute to the insomnia complaint, a comprehensive history should be taken with the patient and, when possible, with the bed partner. This information should include medical and psychiatric history and current medication use, including dosage and time of administration. Possible sleep disorders may present as insomnia, including PLMS and SDB. Identification of the underlying problem causing the insomnia is the key to successful treatment.

A history should also include sleep-related habits such as napping, sleep-wake patterns on weekends versus weekdays, exercise regimens, timing and duration of bright light exposure, and caffeine or alcohol intake. Much of the sleep patterns and habits information can easily be obtained by asking the patient to fill out a sleep log for 1 or 2 weeks. An example of a typical sleep log can be seen in Table 70.1.

Some sleep clinics also use a wrist activity monitor, called an actigraph, which reliably distinguishes sleep from waking based on level of activity to diagnose insomnia. Patients wear this watchlike device and fill out a sleep log for about a week. Contrasting the objective actigraphic-based information with the subjective reports may reveal some misperceptions of the patient regarding their sleep. For example, insomnia patients may overestimate their sleep latency, that is, the amount of time that it takes them to fall asleep and underestimate their sleep efficiency.

Abnormal sleep-wake patterns may indicate a circadian rhythm sleep disorder. These disorders occur when the physiologic propensity for sleep is misaligned with the environmental light-dark cycle. Thus, although sleep may not be disrupted, its timing is inappropriate with respect to the normal environment. Elderly patients often complain of early morning awakenings, which may be caused by advanced sleep phase, that is, they are tired early in the day and they wake up early in the morning, due to an advancement of their sleep-wake cycle. Duffy et al. have suggested that older individuals have a narrow window of time in which sleep is efficiently maintained, and this window is at an advanced clock time relative to younger adults. It is important to stress that although advanced sleep phase may present as insomnia, there is no sleep disruption associated with it, and only the timing of sleep is inappropriate or inconvenient. The differential diagnosis is important in terms of modes of treatment.