Subclinical involvement of central nervous system structures other than motor or sensory tracts in SPG3A and SPG4 patients

OBJECTIVE: Hereditary spastic paraplegias (HSPs) comprise a heterogeneous group of rare, neurodegenerative disorders. The most prominent HSP features: spastic paraparesis, mild somatosensory deficits and bladder dysfunction may be accompanied by additional symptoms i.e.: neuropathy, epilepsy, dementia. We aimed to determine subclinical involvement of nonmotor or sensory brain structures in hereditary spastic paraplegias type 3 A (SPG3A) and type 4 (SPG4). METHODS: Visual evoked potentials (VEPs), brainstem evoked potentials (BAEPs) and electroencephalography (EEG) were performed in 28 SPG4 and 9 SPG3A patients. Disease severity was evaluated with Spastic Paraplegia Rating Scale. RESULTS: The EEG examination revealed abnormalities in 9 SPG4 patients (35%), while it was intact in SPG3A individuals. VEPs indicated mild abnormalities in 38% SPG3A patients: 127.3±7.8ms and 48% SPG4: 122.2±6.4ms. SPG4 patients with DNA microrearrangements in the SPAST gene had statistically significantly longer VEPs latencies (95%CI, 2.78–10.10) and lower amplitudes (95%CI, -5.65 – (-1.45)) than those with single nucleotide variants. BAEPs were distracted accidentally. CONCLUSIONS: It appears that visual tracts, which involve shorter axons than in motor-sensory pathways, are also involved in neurodegenerative processes in SPG3A and SPG4. Additionally, in SPG4 abnormal oscillations of neurons indicated by EEG may probably result from impaired axonal transport.