Correspondence

Painful Sensory Neuropathy

N Engl J Med 2003; 349:306-307July 17, 2003

Article

To the Editor:

Virtually all clinicians I know routinely order tests for vitamin B₁₂ deficiency, folate deficiency, and hypothyroidism as part of the initial workup for peripheral neuropathy. However, none of these disorders are mentioned by Mendell and Sahenk in their Clinical Practice article on painful sensory neuropathy (March 27 issue).1 Are they in fact not truly underlying causes, or is the diagnostic yield so low that testing is not warranted?

Steven Leiner, N.P.
Mission Neighborhood Health Center, San Francisco, CA 94110
sleiner@itsa.ucsf.edu

1 References

1. 1

   Mendell JR, Sahenk Z. Painful sensory neuropathy. N Engl J Med 2003;348:1243-1255
   Full Text | Web of Science | Medline

To the Editor:

Mendell and Sahenk note that in painful neuropathy, only skin-biopsy and quantitative sensory testing can document small-fiber damage but that these tests have limitations. On the basis of a thorough review of the literature that we performed as part of a task force of the European Federation of Neurological Societies to prepare European guidelines for the assessment of neuropathic pain, we believe that laser-evoked potentials also warrant mention. Laser pulses selectively activate A-delta and C nociceptors in the superficial skin layers, thus providing a selective nociceptive input,1 and they evoke scalp potentials that can easily be measured after 10 to 30 stimuli. Laser-evoked potentials have proved to be reliable in assessing nociceptive pathways in peripheral and central neuropathic pain,2-4 and we believe it is the most sensitive and specific test for evaluating small-fiber function. Although this method is not yet widely available, physicians should be aware of it, particularly because it may circumvent the need for biopsy.

Andrea Truini, M.D.
Giorgio Cruccu, M.D.
La Sapienza University, 00185 Rome, Italy
cruccu@uniroma1.it

Luis Garcia-Larrea, M.D.
Hôpital Neurologique, 69003 Lyons, France

4 References

1. 1

   Bromm B, Treede RD. Nerve fibre discharges, cerebral potentials and sensations induced by CO2 laser stimulation. Hum Neurobiol 1984;3:33-40
   Medline

2. 2

   Truini A, Haanpaa M, Zucchi R, et al. Laser-evoked potentials in post-herpetic neuralgia. Clin Neurophysiol 2003;114:702-709
   CrossRef | Web of Science | Medline

3. 3

   Kakigi R, Shibasaki H, Ikeda T, Neshige R, Endo C, Kuroda Y. Pain-related somatosensory evoked potentials following CO2 laser stimulation in peripheral neuropathies. Acta Neurol Scand 1992;85:347-352
   CrossRef | Web of Science | Medline

4. 4

   Garcia-Larrea L, Convers P, Magnin M, et al. Laser-evoked potential abnormalities in central pain patients: the influence of spontaneous and provoked pain. Brain 2002;125:2766-2781
   CrossRef | Web of Science | Medline

Author/Editor Response

In our article on painful sensory neuropathy, we recommend an evaluation that specifically targets causes of conditions affecting the small nerve fibers that mediate pain. Other neuropathies, such as the ones mentioned by Leiner, present a much different clinical picture and would be included in the evaluation of other neuropathic disorders. For example, in vitamin B₁₂ deficiency, the major problem results from loss of function of the large nerve fibers (which normally mediate proprioception and vibration), with accompanying hyperreflexia. Hypothyroid neuropathy also causes injury to the large nerve fibers but results in little or no pain in the arms and legs. Folate deficiency does not cause neuropathy.

Truini and colleagues point out the potential value of laser-evoked potentials in the evaluation of painful sensory neuropathy. This test has important merits, as they indicate, but its availability is currently limited.

Jerry R. Mendell, M.D.
Zarife Sahenk, M.D., Ph.D.
Ohio State University, Columbus, OH 43210
mendell.1@osu.edu

Citing Articles (4)

Citing Articles

1. 1

   G. Masson. (2005) Explorations électrophysiologiques dans les douleurs neuropathiques. Douleur et Analgésie 18:4, 143-149
   CrossRef

2. 2

   E. Hoitsma, J.P.H. Reulen, M. de Baets, M. Drent, F. Spaans, C.G. Faber. (2004) Small fiber neuropathy: a common and important clinical disorder. Journal of the Neurological Sciences 227:1, 119-130
   CrossRef

3. 3

   Massimiliano Valeriani, Paolo Mariotti, Domenica Le Pera, Domenico Restuccia, Liala De Armas, Toni Maiese, Federico Vigevano, Daniela Antuzzi, Giuseppe Zampino, Roberta Ricci, Pietro Tonali. (2004) Functional assessment of A? and C fibers in patients with Fabry's disease. Muscle & Nerve 30:6, 708-713
   CrossRef

4. 4

   A TRUINI. (2004) Laser evoked potentials for assessing sensory neuropathy in human patients*1. Neuroscience Letters 361:1-3, 25-28
   CrossRef