Advancing the Diagnosis of Diabetic Neuropathies: Electrodiagnostic and Skin Autofluorescence Methods

Abstract

Introduction: Diabetic neuropathy (DN) is a generic term for various neuropathies coexisting in a single patient. Clinical diagnosis alone can be misleading, yet routine electrodiagnostic studies in diabetes care are rare. Skin autofluorescence (SAF) is a recognized DN risk factor with potential screening value. This article highlights the diagnostic challenges and raises awareness of the often underdiagnosed neuropathic conditions in diabetes patients.

Material and methods: We present common entrapment neuropathy cases from our diabetes clinic's electrodiagnosis laboratory in Iași, Romania. We selected seven type 2 diabetes patients with sensory or sensory-motor distal polyneuropathy and atypical DN presentations investigated through electroneurography (ENG) and electromyography (EMG) with the Neurosoft^® EMG instrument and SAF measured by standard procedures. Subsequently, a narrative literature review was conducted.

Results: Entrapment neuropathies were diagnosed in all the patients: three carpal tunnel syndromes, two ulnar neuropathies (one proximal, one distal), one peroneal neuropathy, and one case of meralgia paresthetica. The lower-limb cases showed radiculoplexopathy, and there was one case of superficial radial nerve neuropathy. The SAF values ranged from 2.5 AU to 3.4 AU.

Conclusions: Electrodiagnosis is essential for detecting focal neuropathies in patients with sensory-motor distal polyneuropathy. Elevated SAF levels may correlate with symptom severity, although further research, including large cohorts, is needed.

Keywords: AGEs; HbA1c; electroneurography; entrapment neuropathy; skin autofluorescence.

Figure 1

Patient 1. Motor conduction parameters in the right hand (the negative (upwards) action potentials generated by distal, above wrist (1) and proximal, at the elbow (2) stimulation with the active electrode situated on the abductor pollicis brevis muscle, allow us to divide the distance between the 2 stimulation sites (measured in mm) and the conduction time along that specific segment of the investigated nerve (proximal latency—distal latency); hence, the conduction velocity decreased in our patient, 45.3 m/s, suggesting the decrese in conduction velocity from the wrist towards the palm, whereas the conduction between the elbow and the wrist remains stationary). Note—the images are generated with Neurosoft device for EMG.

Figure 2

Patient 1. Stimulation performed above wrist and in mid-palm, with active electrode located on the index finger. Sensory conduction parameters in this right hand (low SNAP amplitudes (both because of the conduction block (first SNAP, 1) and the generalized polyneuropathy (the second SNAP, obtained by stimulation in the middle of the palm, 2, which should have been within normal values if the patient did not have DM), and decreased velocity across the carpal tunnel also suggested by a delayed latency between the two points). The conduction velocity is only 28.8 m/s, along with increased distal latency, 3.8 ms and lower SNAP amplitude (almost 50% compared to the wrist value) Note—the images are generated with Neurosoft device for EMG.

Figure 3

Patient 2. Motor conduction parameters in the left hand, with active electrode placed on the abductor pollicis brevis muscle’s belly (important decrease in the amplitude of the CMAP at the proximal stimulation (2, at the elbow) compared to the distal stimulation (1, above the wrist), visible when stimulating at the elbow, 2), >50%, with motor conduction velocity of only 43.5 m/s. Note—the images are generated with Neurosoft device for EMG.

Figure 4

Patient 2. Sensory conduction parameters in the left hand (low amplitudes of the SNAP with a decrease in the velocity across the tunnel (30.9 m/s), visible when stimulating above the wrist (1) as compared to mid-palm stimulation (2)). Both SNAP amplitudes are decresead here in context of the polyneuropathic condition. Note—the images are generated with Neurosoft device for EMG evaluation.

Figure 5

Patient 2. Neurogenic pattern recored with a concentric needle electrode in the left APB (increased amplitudes, polyphasic morphology; the absence of spontaneous pathologic activity adds up to the chronicity of the described condition).

Figure 6

Patient 3. Focal ulnar neuropathy at the elbow (significant decrease in amplitudes of CMAPs when stimulating across the elbow, orientating the confirmation of the diagnosis).

Figure 7

Patient 4. Comparative peroneal motor nerve conduction studies, with motor stimulation at ankle level (1), at the fibular head level (2) and above the knee (3) (lower amplitudes at the proximal stimulation sites (2 and 3), especially above the fibular head (3) on the affected side (>50%). Recording is being performed here with the active electrode situated on the extensor digitorum brevis mucle. The temporall dispersion suggested by the decrease of amplitude (2) is also in context of the sensory-motor polyneuropathy. Note—the images are generated with Neurosoft device for EMG.

Figure 8

Patient 5. Superficial radial nerve evaluation (decreased sensitive conduction velocity, 46.4 m/s when stimulating in the middle 1/3rd of the forearm and collecting on the first interdigital space). Note—the images are generated with Neurosoft device for EMG.

Figure 9

Patient 6. Right lateral femoral cutaneous nerve (decreased amplitudes on both sides, significantly reduced on the right, along with decreased velocity, 31.9 m/s). The stimulation is performed at anterior superior iliac spine level, with recording at about 12 cm on an imaginary line connecting the stimulation point with the lateral pattelar side. Note—the images are generated with Neurosoft device for EMG.

Figure 10

Patient 7. Motor inching across the right Guyon tunnel suggesting the decrease on amplitudes of CMAPs across the wrist’s stimulation points, with a significant decrese >50%. Note—the images are generated with Neurosoft device for EMG evaluation and it reports commas instead of dots and hyphen (-) instead of minus sign.

Figure 11

Evolution of the HbA1c levels in the examined patients.