A study of F‐waves in patients with unilateral lumbosacral radiculopathy

Abstract

Our results show that the use of F-waves may improve the electrodiagnosis of the ULSR if the number of repeater waves is evaluated given the clear and consistent increase of this variable in patients with lumbosacral root injury.

Usefulness of assessing repeater F‐waves in routine studies

“…The comparison between patient groups in all three nerves did not point to an association of increased total Freps with any particular pathological condition among those studied here. Irrespective of the absolute numbers of repeater F‐waves, the mean difference between healthy controls and patients with CTS, ALS, or L5 root lesion found in this study were proportionally similar to those previously reported 2–5. Repeater F‐waves have not been systematically assessed in polyneuropathies; only one report described 3 patients with diabetic polyneuropathy and showed an increased frequency of RNs 12…”

“…For the ulnar nerve, using 100 stimuli in 11 healthy volunteers, Guiloff and Modarres‐Sadeghi11 reported a mean value of index RN of 11.2 ± 4.9, which was reduced to 5.7 ± 6.0 when samples of 20 stimuli were assessed; similarly, using 200 stimuli in 21 subjects, Peioglou‐Harmoussi et al3 estimated the median value of RN to be 3.3 (min–max: 1.1–5.4), as compared with our median value of RN of 0 (5th–95th percentile: 0–2.4). Pastore‐Olmedo et al5 found a mean value of persistence of total Freps of 18.6 ± 15.7 in the fibular nerve of 5 healthy subjects using 30 stimuli, as compared with our median value of 0 (5th–95th percentile: 0–22). These comparisons should be interpreted with caution due to the different statistical variables employed in different studies.…”

“…Taking into account the infrequent backfiring of each neuron, the statistical chance of two or more neurons backfiring together on two or more occasions in a sample of 20 stimuli is close to zero. Therefore, we suggest that each individual F‐wave occurring repeatedly is generated by backfiring of a single neuron, justifying the term “RNs.” When searched for latency and amplitude changes between subject groups, the RN values were expressed as ratios to the corresponding values of all F‐waves in a given nerve, in order to adjust for the overall F‐wave abnormalities documented specifically in the DM‐PN, ALS, and L5‐Rd groups 5, 17, 18. These ratios remained stable in all groups and were unaffected by the diverse diseases examined.…”

“…A higher‐than‐normal frequency of repeater F‐waves has been demonstrated in a small number of patients with motor neuron disease and cervical spondylolysis,3 as well as in a large sample of patients with carpal tunnel syndrome (CTS) 4. More recently, larger numbers of repeater F‐waves were also shown in patients with lumbosacral radiculopathy when compared with healthy individuals 5. The clinical significance of repeater F‐waves as a sign of nerve pathology and their usefulness in daily electrodiagnostic routines has not been evaluated, because all studies so far have compared individual conditions to normal and not to each other.…”

Utility of minimum F‐wave latencies compared with F‐estimates and absolute reference values in S1 radiculopathies: Are they still needed?

“…Studies have shown a wide range of sensitivities (18–74%), depending on the nerve root involved, the F‐wave parameter analyzed, and reference values used . Various F‐wave parameters have been studied, including minimum, maximum, and mean latency, as well as persistence, chronodispersion, duration, and number of repeater F‐waves . Although each of these parameters can provide meaningful information regarding conduction in proximal axons, the minimum reproducible latency compared with an absolute reference value is the measurement that is recorded most efficiently and reported most widely in clinical practice.…”