ABSTRACT
OBJECTIVE: To determine whether 5 Hz and 2000 Hz sinusoidal electric currents evoke different sensations and to indirectly evaluate which peripheral nerve fibers are stimulated by these different frequencies. METHODS: One hundred and fifty subjects chose three among eight descriptors of sensations evoked by 5 Hz and 2000 Hz currents and the results were submitted to factor analysis. In 20 subjects, reaction times to 5, 250 and 2000 Hz currents were determined at 1.1 x ST and reaction times to 5 Hz currents were also determined at 2 x ST. RESULTS: Responses were grouped in four factors: Factor 1, which loaded mainly in descriptors related to tweezers stimulation, was higher than the other factors during 2000 Hz stimulation at 1.5 x ST. Factor 2, which loaded mainly in descriptors related to needle stimulation, was higher than the other factors during 5 Hz stimulation. Factor 1 increased and Factor 2 decreased with an increase in 5 Hz intensity from 1.5 to 4x ST. Reaction times measured from the fastest responses were significantly different: 0.57 s (0.16 to 1.60), 0.34 s (0.12 to 0.71) and 0.22s (0.08 to 0.35) for 5, 250 and 2000 Hz, respectively, and 0.22s (0.11 to 0.34) for 5 Hz at 2 x ST. CONCLUSIONS: Sinusoidal electrical stimulation of 5 Hz and 2000 Hz evoke different sensations. At juxta-threshold intensities, RT measurements suggest that 2000 Hz stimulates Abeta-fibers, 250 Hz Abeta- or A partial differential-fibers, 5 Hz Abeta-, A partial differential- or C-fibers. The fiber type, which was initially stimulated by the lower frequencies, depended on inter-individual differences.
Subject(s)
Electric Stimulation/methods , Nerve Fibers, Myelinated/physiology , Nerve Fibers, Unmyelinated/physiology , Reaction Time , Touch/physiology , Adolescent , Adult , Electric Stimulation/adverse effects , Female , Humans , Male , Middle Aged , Pain/etiology , Pain/physiopathology , Paresthesia/etiology , Paresthesia/physiopathology , Pressure , Reference Values , Sensory Thresholds , Vibration , Young AdultABSTRACT
Homocystinuria presenting as cerebral venous thrombosis is not usual. We report on a 13-year-old boy who was admitted to the hospital due to severe headache, nausea, vomiting and fever (38 degrees C). The patient was Marfan like and presented left hemiparesis and meningeal irritation sings. He was mentally retarded, had severe myopia, and had right lens dislocation one month before. Cranial CT scan was suggestive of cerebral venous infarct. MRI and magnetic resonance angiography showed venous infarcts more prominent in the right thalamic projection with hemorrhagic transformation and multiple foci of cortical (occipital and parietal bilaterally) deep parietal and left capsular bleeding, secondary of thrombosis of the transverse and sigmoid venous sinuses. High levels of homocysteine were detected in the blood and urine. Homocystinuria is an autosomal recessive inborn error of methionine metabolism caused by cystathionine-beta-synthase defect in most cases. We discuss the clinical and radiological findings in this patient, analyzing the pathophysiology of the thrombotic events related to homocystinuria.
