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Baclofen (also known as Lioresal®) has long been prescribed to treat muscle spasticity in people living with spinal cord injury (SCI) and multiple sclerosis.  Recent findings from the laboratory of Dr. Christine Thomas, a faculty member of The Miami Project to Cure Paralysis at the University of Miami, demonstrate that long-term use of Baclofen can actually have unwanted effects on paralyzed muscles in people living with chronic SCI.  In a recently published peer-reviewed research article in the journal Brain (2010, 133: 117-125), Dr. Thomas and members of her lab evaluated and compared the contractile properties of small units of the thenar (thumb) muscles in three group of people, 1) those with a chronic cervical SCI who had taken Baclofen for an average of 7 years (23 units from 5 people), 2) those with a chronic cervical SCI who had not taken Baclofen for an average of 10 years (25 units from 7 people), and 3) those without a SCI and in healthy condition to serve as control subjects (48 units from 12 people).  They found that the SCI + Baclofen group had significantly weaker and slower muscle contractions and slower conducting nerves innervating the muscle fibers compared to the control groups.

Muscle spasticity develops in many people with SCI.  The body has reflexes built into the spinal cord, which are controlled by the brain, that are used automatically to identify sensations and tell the body how to react.  For example, if something hot were to touch the leg, reflexes would be responsible for immediately withdrawing the leg from the heat source.  After SCI, regulation of these reflexes by the brain is lost.  As a result, the spinal cord alone tries to regulate the reflexes and often ends up sending exaggerated signals back out to the muscles.  The outcome is hyperactivity of the nerves and muscles, or spasticity.  Baclofen is a muscle relaxant that works by inhibiting the reflexes at the spinal cord level.  It is not selective for just hyperactive reflexes, however.  It inhibits or depresses many aspects of the central nervous system.  As a result, it can be effective at reducing severe muscle spasticity, but it also produces common side effects such as drowsiness, dizziness, slurred speech, and confusion.  New, long-term side effects revealed by our study are muscle weakness and fatigability.

What do these research findings mean?  These results suggest caution in treatment with baclofen, particularly if it causes loss of function.  Chronic baclofen use may weaken any remaining voluntary muscle force, any force generated during functional electrical stimulation, and muscle spasms.  Thus, the acute effects of baclofen, whether positive or negative, have to be weighed carefully in relation to its potential long-term impact on neuromuscular properties.  We do not recommend for anyone to immediately stop taking Baclofen.  In fact, the FDA has previously issued the following black box warning about Baclofen withdrawal:  “Avoid abrupt withdrawal of the drug; abrupt withdrawal of oral or intrathecal baclofen has resulted in severe sequelae (hyperpyrexia, obtundation, rebound/exaggerated spasticity, muscle rigidity, and rhabdomyolysis), leading to organ failure and some fatalities.  Risk may be higher in patients with injuries at T-6 or above, history of baclofen withdrawal, or limited ability to communicate.”  Rather, we suggest that further research regarding the negative consequences of long-term Baclofen use is warranted.  It may be the case that rehabilitation strategies aimed at restoring the strength, fatigue resistance, and speed of paralyzed muscles may need to be tailored differently for individuals that have been using Baclofen chronically, especially in regard to stimulus intensity, frequency, and training duration.

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