Dr John Fink, SPF Medical Advisor
Progressive worsening in hereditary spastic paraplegia (HSP) is extremely variable and multifactorial. Often (though not always) when HSP symptoms begin in very early childhood (infancy), there is very little if any worsening.
Some genetic forms of HSP tend (though not always) to have first symptoms very early (infancy). For these forms of HSP (eg, SPG3A/atlastin mutation HSP), it is common to have very little worsening. For many of these individuals HSP resembles cerebral palsy in so far as having very little worsening. For the most common genetic forms of HSP (eg. due to SPG4/spastin mutation), symptoms begin after childhood. For these individuals, it is very common for symptoms to gradually increase (slow, insidious progression).
It is important to note that whether symptom worsening occurs at all; or if present, the rate at which symptoms become worse, reflects at least four potential processes:
Worsening of the underlying condition (axon degeneration of selected spinal cord nerves)
The ability of the nervous system to compensate for (and recover from) dysfunction of these nerves (ie. the "plasticity of the nervous system" which is generally superior in infancy)
The emergence and worsening of spasticity and tendon shortening
General musculo-skeletal and cardio-pulmonary de-conditioning.
Progressive spasticity may occur (and cause worsening of symptoms) even though the underlying nerve injury/nerve dysfunction is not getting worse. Consider for example an individual who suffers a stroke (cerebrovascular accident). Within seconds to minutes nerve cells die. However, spasticity and tendon shortening are not present at the beginning but rather develop slowly over months and years.
For HSP, it is likely that often (though not always), an important component of "worsening of symptoms" is due to "worsening of spasticity" (which does not necessarily mean that the underlying condition is progressing rapidly). This concept is one of the reasons why muscle stretching and muscle relaxing medications are prescribed.
Musculo-skeletal and cardiopulmonary deconditioning affect all of us. Individuals with sedentary lifestyles and especially those in wheelchairs are particularly at risk. It is likely that general musculo-skeletal and cardiopulmonary de-conditioning contribute to age-dependent decreased endurance and strength in HSP.
Given the many different genetic forms of HSP, the varying ages of symptom onset, the varying severity of symptoms, and the variable exercise and physical fitness of an individual, it is not possible to predict whether a given individual will experience "obvious worsening of symptoms"; or instead experience "relatively little worsening".
John K. Fink, M.D.
Professor, Department of Neurology
University of Michigan
Saturday, September 8th, 2012