**4. Discussion**

We also performed an analysis of the initial positivity on 39 different end plate spikes and 33 different fibrillation potentials. 14 out of the 39 end plate spikes had an initial positive deflection, with the mean duration 0.5 ms, SD 0.17, and range 0.3-0.9 ms. The rest had a negative onset. All 33 fibrillation potentials had an initial positive deflection, with mean duration 1.6 ms, SD 0.4, and range 0.6-2.4 ms. Thus, when an initial positive deflection was observed in end plate spikes, it was significantly (t= 9.9; p<0.001) shorter than that of fibrillation potentials. The

Table 1 presents the mean characteristics in different fibrillation potential categories and the significance of difference of the variables compared to end plate spikes. Table 2 presents the

N 41 13 13 12 15

Intervals (ms) mean SE mean SE mean SE mean SE mean SE

mean 510\*\*\* 43 223 37 556\* 191 142 37 130 42

median 387\*\*\* 37 209\* 39 548\* 190 104 30 95 31

minimum 159\*\*\* 14 148\*\*\* 25 513\*\*\* 186 25\* 5 12 3

maximum 1406\*\*\* 127 412 49 637 199 736 204 578 163

**Regularity**

APCID 151 7 52\* 6 5\*\*\* 1 128\* 14 175 13

MCD 358\*\*\* 42 47 7 13\* 5 111 36 116 42

**Potential**

Ampl (µV) 145 13 120 14 117 19 169 36 128 14

Spike duration 2.3 0.1 3.1 0.4 2.4 0.1 2.5 0.2 2.8 0.4

**Table 1.** Interval, regularity and potential variables of different spontaneous activity categories. "With pauses": slightly

(ms)

\* p ≤ 0.05 compared to end plate spikes

irregular fibrillation potentials with pauses.

\*\*\* p ≤ 0.001 \*\* p ≤ 0.01

**Fibrillations Neurally driven sequences Random With pauses Regular "Myokymic" End plate spikes**

95 % confidence interval for difference was 0.8 to 1.2 ms.

48 Electrodiagnosis in New Frontiers of Clinical Research

differences between variables of different fibrillation categories.

#### **4.1. Firing patterns of fibrillation potentials**

Denny-Brown & Pennybacker (1938) described the periodic contractions of denervated muscle fibres as true fibrillations and differentiated fibrillation from fasciculations and myokymia. Jasper & Ballem (1949) found positive sharp waves, often in combination with fibrillation potentials and claimed that they may represent local potentials set up at the needle point by the injury. They stated that positive sharp waves do not occur in a normal muscle. Kugelberg & Petersén (1949) also described positive sharp waves, "synchronized activity" in totally denervated muscles as well as fibrillation potentials of both constant frequency (regular fibrillations) and "repetitive fibrillary activity", i.e. slightly irregular fibrillations with pauses (see Results). It was claimed that only rhythmic, regular fibrillation potentials have clinical significance (Stöhr 1977). However, also irregular fibrillations do exist, and in fact there are several types of them. Irregular fibrillations do not usually change their firing pattern during the time of an EMG recording. The incidence of irregular fibrillations reported in literature is very variable. Heckmann & Ludin (1982) pointed out that even in totally denervated muscle irregularly firing potentials may be found (in canine muscle), and Buchthal & Rosenfalck (1966) stated that half of the fibrillation potentials whose discharge pattern was examined appeared irregular. In fact, the period of time after nerve or muscle injury seems to be essential. Approximately half of fibrillation sequences were irregular 30 days after muscle injury, while in more recent injuries the sequences were mainly regular (Partanen & Danner 1982). My experience in clinical ENMG work is that irregular fibrillations are most common 1 – 3 months after axonal injury and in extreme cases only a number of irregular fibrillation sequences may be present with no regular fibrillations at all (unpublished personal observation). There may also be mixed forms of fibrillations, with mainly regular rhythm but sudden changes of the interval (Partanen & Danner 1982, Conrad et al. 1972).

when they are propagated outside the end plate zone and thus the form of the potential is indistinguishable from that of a fibrillation potential (Buchthal & Rosenfalck 1966). We note that there is a distinct difference between the wave forms of end plate spikes and fibrillation poten‐ tials. The former show either a negative onset or a short positive onset, whereas fibrillation potentialsshowapositiveonsetwhichalwaysislongerthanthatofendplatespikes(seeResults). However, the amplitude and spike duration of fibrillation potentials and end plate spikes are similar (Table 1). We have observed fibrillation potentials with negative onset, (mainly as "negative sharp waves", obviously cannula-recorded positive sharp waves with inverted polarity),butthesearerareanddonothappentobepresentinthematerialcollectedforthiswork. This fact is not in concert with the data published earlier, which state that a considerable number of fibrillation potentials may have a negative onset (Buchthal & Rosenfalck 1966, Heckmann & Ludin 1982). In any case fibrillation potentials and end plate spikes may be distinguished both

Different Types of Fibrillation Potentials in Human Needle EMG

http://dx.doi.org/10.5772/55352

51

**Figure 7.** The positive deflection before the main spike component (pair of arrows) is shorter in averaged end plate spike (EPS) than in averaged fibrillation potential (fibr). The averaged mean potential is shown with ± 1 SD curves.

The formation of the shape of end-plate spikes was extensively studied by Dumitru (2000) according to the needle irritation hypothesis of peripheral nerve branch or nerve terminal (tip or shaft irritation of the terminal nerve). He explained the formation of biphasic and triphasic

From Partanen, J. (1999), Author´s own work.

by the firing pattern and the wave form at the onset of the potential (Fig. 7).
