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Spastic (flaccid paresis) of the lower limbs: causes, symptoms, diagnosis, treatment
Last reviewed: 06.07.2025
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Symmetrical predominantly distal weakness (spastic or flaccid paresis) of the lower extremities
This is a special category of patients with distal weakness in the legs. As a rule, such diseases lead to dysbasia. It is always useful to remember that among the causes of distal lower paraparesis, not only polyneuropathy is known, but also processes at the muscular, spinal and even cerebral levels.
[ The main causes of spastic (flaccid paresis) of the lower limbs:
- Parasagittal tumor or (rarely) cortical atrophic process.
- Spinal cord lesions (extramedullary and intramedullary).
- Progressive spinal muscular atrophy.
- Amyotrophic lateral sclerosis (lumbosacral form).
- Lesions of the spinal cord conus and cauda equina.
- Hereditary motor-sensory polyneuropathy types I and II (Charcot-Marie-Tooth amyotrophy).
- Myopathies.
- Polyneuropathies.
- Bilateral peroneal nerve lesion.
Medial cerebral hemisphere damage.
Processes involving the precentral gyrus bilaterally may cause spastic, predominantly lower distal paraparesis. The etiology is similar to that described for lower spastic paraparesis syndrome.
Spinal cord lesions.
This process causes predominantly distal spastic paraparesis only when there is a bilateral extramedullary lesion of the spinal cord involving the corticospinal tract and, in particular, the superficial fibers going to the lower extremities. An intramedullary process (tumor or syringomyelia) in the lower lumbar or upper sacral spinal cord may affect the anterior horn cells involved in the innervation of the muscles of the lower extremities (leading to slowly progressive flaccid paralysis, always accompanied by sensory loss, often with urinary disorders). Such lesions are clarified by MRI, lumbar puncture and myelography.
Progressive spinal amyotrophy.
In spinal muscular atrophy, the distal leg muscles are rarely involved first, but when they are involved, it is often symmetrical. The diagnosis is confirmed by EMG testing, which indicates a neuronal level of damage with unchanged nerve conduction velocities.
Lumbosacral form of amyotrophic lateral sclerosis.
This form of amyotrophic lateral sclerosis begins with asymmetric weakness and atrophy of the distal parts of the legs (usually starting with one leg, then the other is involved), fascicular twitching in them, then an ascending course is detected with diffuse EMG signs of anterior corneal damage and the addition of symptoms of upper motor neuron damage.
Lesions of the conus and cauda equina.
Such damage, causing bilateral distal flaccid paresis of the legs, is always accompanied by severe sensory disturbances and urination disorders.
Hereditary motor-sensory polyneuropathy types I and II (Charcot-Marie-Tooth amyotrophy).
Variants of Charcot-Marie-Tooth amyotrophy are manifested exclusively by bilateral, distal atrophy of the leg muscles with paralysis or paresis of the feet (a familial disease, progresses very slowly, there is a high arch of the foot, no Achilles reflexes, well-developed thigh muscles ("stork legs", "inverted bottle"). The arm muscles are involved later, vibration sensitivity may be impaired distally in the lower limbs; in type I, the speed of excitation conduction along the nerve may be significantly reduced.
Myopathies.
Rarely, myopathy results in symmetrical distal or predominantly distal weakness; variants include Steinert-Batten myotonic dystrophy and Welander (and Baymond) congenital distal myopathy. Such syndromes result in purely motor deficits and often involve the upper extremities.
Polyneuropathies.
In most polyneuropathy of various origins, weakness both at the onset of the disease and later is, as a rule, distal, often accompanied by paresthesia, subjective sensory disturbance, foot drop and "steppage", absence of Achilles reflexes, and characteristic changes in EMG.
Bilateral symmetrical lesion of the peroneal nerve.
This lesion due to mechanical compression (found in patients who were unconscious, as well as in the presence of other risk factors) leads to bilateral involvement of the muscles of the anterior tibial region only, paralysis of the peroneal muscles (without involvement of the gastrocnemius muscles, with preservation of the Achilles reflexes), loss of sensitivity on the dorsum of the foot and lateral surface of the leg.