Validation of the Modified LDIFlare Technique: A Simple and Quick Method to Assess C-fiber Function
Muscle & Nerve: Volume 47, Issue 3,
pages 351–356, March 2013
Prashanth R.J. Vas MBBS, Gerry Rayman MD
Dr. Gerry Rayman’s UK-based team developed a method to assess C-fiber function by measuring the axon reflex-induced flare using a laser Doppler imager after heating the skin in the feet to 44°C. It is called the “laser Doppler imager flare technique” (oLDIf*).
Despite its utility, the study is quite time-consuming. Therefore, the team modified the method (mLDIf**) by heating the skin to 47°C, which shortened the study to 30 minutes or less and made the technique more suitable for clinical use. They studied mLDIf in 5 healthy controls before and after local anesthesia, diabetic patients with neuropathy (DN+
, n=10), and diabetic patients without neuropathy (DN−
, n=16). They found that mLDIf was reduced in DN−
compared with control subjects, (6.8 ± 2.8 vs. HC, P
= 0.003); it was markedly reduced in DN+
compared with healthy controls, as well as DN−
(2.0 ± 1.1 vs. HC and DN−
< 0.0001). Local anesthesias almost abolished the flare (9.3 ± 3.0 cm2
vs. 1.7 ± 0.3 cm2
Structural and functional changes of unmyelinated C-fiber nerves precede large fiber impairment in diabetic neuropathy. Modalities, such as autonomic testing (including quantitative sudomotor axon reflex testing or QSART), skin biopsy with intraepidermal nerve fiber density measurement, quantitative sensory testing, and confocal microscopy, have been utilized to assess C-fiber function. The authors report a modified technique utilizing the mLDIf, which provides an objective and quantifiable assessment of peripheral afferent and efferent C-fiber function (vs. QSART measurement of only efferent sympathetic fibers).
This preliminary study confirms the reproducibility of the modified technique, which considerably shortens study time, potentially making it more suitable for widespread clinical use. However, larger studies are necessary to better define the role of this technique in the evaluation of peripheral neuropathy.
* O for “original,” Diabetic Care
**M for “modified”