SDB & PLMD: What Does it Mean?

By Kerrin Leon White - March 20, 2001

SDB, PLMD, UARS, OSA, CPAP, AHI...

Are you confused by all the acronyms used by sleep researchers and even ordinary people who are "into" sleep disorders?

I hope so; I hope your curiosity to understand this combination of acronyms works to get you reading about a subject which, if I spelled the words out, would sound unbelievably boring, but which really has relevance to many people with SDB (Sleep Disordered Breathing, which includes Sleep Apnea and the closely related disease called Upper Airway Resistance Syndrome or UARS--another acronym for you to learn! PLMD, in case you didn't know already, stands for Periodic Limb Movements of Sleep.

At the risk of losing you for good, I will go on to mention the recently published research report that stimulated me to write this article. It is entitled "The Association of Upper Airway Resistance with Periodic Limb Movements," and was authored by two researchers at the University of Mississippi Medical Center: Elliott N. Exar, MS, and Nancy A, Collop, MD. I found it in the journal Sleep (Volume 24, Number 2, pages 188-192, March 15, 2001).

In case your curiosity continues to overcome your confusion, let me jump ahead. For quite a while, sleep doctors have noticed that people with sleep apnea controlled on CPAP (Continuous Positive Airway Pressure) sometimes developed PLMD, which can disrupt sleep in a way similar to apneas and hypopneas. This study claims to be the first to show an association between PLMD and UARS, which can be roughly thought of as a kind of minor, maybe fledgling, form of sleep apnea. UARS involves no stoppage, or even reduction, of breathing, but it does involve enough obstruction to require extra effort to continue breathing, and that effort can disrupt the continuity of sleep much as do apneas and hypopneas--and PLMD.

So what? Remember that PLMD often appears only after sleep apnea is controlled by CPAP. The apneas and hypopneas somehow appear to "cover up" the PLMD--or is that the wrong way of thinking about this development?

UARS, being less severe than sleep apnea, might not "cover up" an association between SDB and PLMD.

The researchers studied 20 patients with PLMD who underwent overnight laboratory sleep studies. They eliminated most people with diagnosable sleep apnea by excluding patients who turned out to have an Apnea/Hypopnea Index (AHI) above 10.

Nevertheless, 14 (70%) of these 20 PLMD patients showed evidence of UARS. The majority (63%) of arousals related to difficulty breathing were associated with a PLMD--that is, they tended to occur at the same time. In other words, SDB tended to go with PLMD in individuals, and single events of effortful breathing also tended to occur at the same time as PLMD for each individual.

The authors point out that cases of PLMD who remain sleepy despite medications to control the PLMD, may be continuing to have sleep disruption due to a different cause--in this case, the subtle illness called UARS. Likewise, patients with diagnoses of SDB who remain sleepy despite CPAP may be having PLMD disrupt their sleep.

However, what I want to emphasize about this, is that we should beware of thinking of ourselves as "a sleep apnea patient" or "a PLMD patient." Sleep--and its disruption--is affected by many different factors. These are only two; I am certain there are many more.

For more information on Sleep Apnea, please see our Sleep Apnea Section.