Modifica di Clinic Electromyography (sezione)

====IP Analysis Methods====
Electromyographers generally interpret IP signals subjectively, observing the signals on an oscilloscope screen or listening to the sounds on audio.<ref name="Walton">Walton JN.: The electromyogram in myopathy: analysis with the audio-frequency spectrometer. J. Neurol Neurosurg Psychiatry. 1952; 15: 219-26.</ref> To reduce subjective interpretation, different schools have developed various methods for objective analysis of the interference pattern, such as quantitative analysis based on recognizing the sound frequency emitted by MUP and IP activity;<ref name="Willison">Willison RG. Analysis of electrical activity in healthy and dystrophic muscle in man. J. Neurol Neurosurg Psychiatry. 1964; 27: 386-94.</ref> frequency-domain analysis, which is based on recognizing the visual analog signal and mathematical processing of the amplitude/frequency ratio of the EMG signal; spectral analysis of frequency, which uses a digital method employing Fourier transform algorithms; time-domain analysis, which, compared to the previously described methods, recognizes the number of peaks per unit of time, expecting a higher number of peaks in myopathic patterns.

A more recent mathematical implementation is Willison's method,<ref name="Willison" /> which developed an automatic IP analysis system called "turns/amplitude analysis". This method measures the number of turns in the IP signal and the mean amplitude differences between successive turns (MA). A turn occurs at each positive or negative peak, and subsequent turns occur at peaks in the opposite direction. To exclude small amplitude peaks, resulting from background noise, a turn is defined as a signal modification of at least 50 μV between successive turns. In partial chronic denervation situations, the MA increases without changes in the number of turns (NT). This is attributed to the increased density of muscle fibers within the motor unit due to reinnervation.

Fuglsang-Frederiksen<ref name="Frederiksen">Fulgsang-Frederiksen A et al.: Diagnostic yield of the analysis of the pattern of electrical activity and of individual motor unit potentials in myopathy. J. Neurol Neurosurg Psychiatry. 1976; 39:742-50.</ref> measured the NT and MA values and calculated the NT/MA (T/A) ratio and the incidence of short-duration intervals between successive turns. In myopathy patients, they demonstrated that the diagnostic value of T/A analysis is equivalent to MUP analysis. In 80% of the myopathy studies presented, the T/A ratio was characterized by a marked increase in the NT/MA ratio. In neuropathy, this ratio decreases due to a significant reduction in the number of turns attributed to the increased MUP duration. The limitation of this type of analysis is data reproducibility only at comparable muscle contraction levels, so the examination is limited by the need to monitor force.
**Clouds Analysis**
Stolberg and collaborators developed a computerized T/A analysis system that does not require monitoring contraction force. IP signals are recorded from 6-10 sites in the examined muscle at 3-5 force levels ranging from minimum to maximum for each site. NT and MA values are measured from each of the 20-40 epochs, and a plot of the MA/NT ratio is created for each epoch. An area of this plot called the “Normal Cloud” is defined as the part that contains more than 90% of the points from a reference population. A discrepancy greater than 10% of the analyzed points that fall outside the normal cloud is considered abnormal. Myopathy patients have more points in the lower part of the “normal cloud,” while in neuropathy, the points are located in the upper side of the normal value or outside the normal curve (Fig. 5, 6, 7).<gallery mode="slideshow">
File:Figure 5 (Iani).jpg|'''Figure 5:''' Interference pattern EMG trace in a patient with myopathy. Early low-amplitude recruitment is observed. The lower panel shows the plot of the Cloud method (see text).
File:Figure 6 (Iani).jpg|'''Figure 6:''' Neurogenic-type EMG trace. Single oscillation motor units of large amplitude and increased duration are observed. The full interference pattern is not achieved with maximal voluntary contraction.
File:Figure 7 (Iani).jpg|'''Figure 7:''' This series of graphs represents the Cloud plots in neurogenic (upper) and myopathic (lower) pathologies. In the first panel, it is observed that in the neurogenic pattern, the plot points fall above the normal cloud, while in the myogenic pattern, they fall below. 
</gallery>

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