Jennifer Theunis1, David Black1, Arnaud Degouy1, Anne-Marie Schmitt1 and Laurent Misery2

1Pierre Fabre Research Institute, Toulouse, and 2Department of Dermatology, University of Western Brittany, Brest, France

The role of personal factors makes it difficult to correlate subjective data, such as those obtained with the use of a visual analogue scale, and objective data, such as a quantity of injected histamine. In this study, prick tests with histamine and codeine on the forearms allowed a coherent variation in itch scores to be obtained over time, with highly significant differences from controls and with a peak at 4 minutes. These tests are therefore valuable for screening anti-pruritic agents. A significant difference between initial scores and scores for new prick tests after 7 days suggest that tachyphylaxis persists.

(Accepted March 13, 2008.)

Acta Derm Venereol 2008; 88: 455–457.

Laurent Misery, Department of Dermatology, University Hospital, FR-29609 Brest cedex, France. E-mail: laurent.misery@chu-brest.fr

The measurement of itch (1, 2) is difficult because itch or pruritus is a subjective sensation defined by its association with a need to scratch. Nonetheless, it is necessary to measure itch for the follow-up of some patients and in clinical studies. Itch can be measured through complex recording of scratch movements or, more simply, through the use of scales. Recently, a very fine scale was defined (3) and validated (4): the Itch Severity Scale (ISS). Yet, the most frequently used itch scale is the traditional visual analogue scale (VAS).

To assess the clinical efficacy of anti-pruritic components, there is a need for experimental induction of itch, through electrical or mechanical stimulation or primarily by the intradermal injection of itch inducers (2). Among them, histamine is the most widely used.

The measurement of itch after its induction in humans is difficult to assess because perceived itch is related to both peripheral (injection of histamine) and central factors. Indeed, the role of personal, emotional and psychological factors and the activation of motor areas (need to scratch) are very important in the central integration of itch in the brain. These allow us to define itch as “a sensation accompanied by the contralateral activation of the anterior cortex and the predominantly ipsilateral activation of the supplementary motor areas and the inferior parietal lobule; scratching may follow” (5), reflecting the fact that “it is the brain that itches, not the skin”(6).

Hence, it could be difficult to correlate subjective data, such as those obtained with the use of a VAS (from 0 to 10) with objective data, such as a quantity of injected histamine. This is why authors have preferred to search for a correlation with skin blood flow (7, 8) or, more recently, with functional magnetic resonance imaging data (9, 10), without a measured level of intensity, or both (11). To our knowledge, there was no validated protocol that uses prick-tests and VAS allowing further clinical trials. In this work, we have measured itch intensity at different times following prick-tests with histamine and codeine in a randomized double-blinded study.

Subjects and methods

This study was approved by the ethics committee of Brest. Thirty-six men, age range 18–30 years, with phototypes I, II or III, were included in the study. They did not use any cosmetics on the studied areas from one week prior to the initiation of tests nor any anti-inflammatory drug within one week, any anti-histamines within three weeks, any topical or systemic steroids 2 months prior to the study or psychopharmacological drugs 2 years prior to the study. They had no antecedents of atopic, allergic or neurological disease and had no skin lesions or scars on their forearms.

A screening visit was organized one week before the first tests. It was required that participants wash their skin in the evening prior to testing. At their second visit, prick-tests were performed on each forearm. Two areas of 1 cm2 were marked 10 cm apart on each volar aspect. Four prick tests were performed with a polymethacrylate lancet (Stallerpoint®, Antony, France) in the middle of these areas: one without any product, one with NaCl (1 µl, 0.9%), one with histamine chloride (1 µl, 10 mg/ml, Stallergènes, Antony, France) and one with codeine phosphate (1 µl, 9%, Stallergènes). The order of prick tests was randomized. The diameter of induced papules was measured to ensure that tests were performed accurately: greater than 4 mm 20 min after histamine or codeine prick tests, and smaller than 3 mm after NaCl prick tests. Subjects evaluated itch intensity (from 0 to 10) by using the classic VAS after 1 min (T1), 2 min (T2), 4 min (T3), 10 min (T4), 20 min (T5) and 30 min (T6). Scratching was forbidden. At the third visit, 7 days later, the same prick tests were repeated with VAS assessment times being recorded as T11, T12, T13, T14, T15 and T16, respectively.

Descriptive, intra-group (comparing results from the second and third visits) and inter-group (comparing areas) analyses were carried out. Statistical analysis was made by analysis of variance, Bonferroni, Tukey, Student’s t-test and Wilcoxon tests.

Results

Thirty-six men were enrolled in the study (average age 24.5 years), with one subject who missed the third visit. Prick-tests were correctly performed in all subjects: diameters of papules were greater than 4 mm 20 min after histamine or codeine prick tests, and less than 3 mm after NaCl prick tests with no papules observed in areas where a prick test was performed without product.

VAS results were variable according to each patient. Intra- and inter-group comparisons showed significant differences (p < 0.05). After prick tests with histamine chloride or codeine phosphate, VAS scores were better than 0 at all times, at the second visit (day 0) and the third visit (day 7). There was no itch in the untreated area, but a weak increase 1, 2 and 4 min after application of NaCl.

In comparison with the untreated area, histamine chloride induced a significant itch at all measurement times and codeine phosphate inducing a significant itch from 1 to 20 min, whereas there was no significant difference with NaCl. In comparison with NaCl, prick tests with histamine chloride induced a significant difference at all times measured and those with codeine phosphate induced a significant difference from 2 to 20 min. A significant difference between histamine and codeine salts was noted only at 1 min.

At days 0 and 7, mean values of the VAS scores increased from T0 to 4 min then decreased (Fig. 1 A and B). A similar change in these scores was noted in the 3 cases, but VAS scores remained near 0 without the addition of a product. Statistical analysis showed significant decreases in VAS scores between the second and third visits for histamine (p < 0.005), codeine (p < 0.01) and NaCl (p < 0.005), whereas there was no modification in non-injected areas (Table I). No significant differences were found in the diameters of papules.

Fig. 1. Visual analogue score (VAS) scores at (a) day 0 (n = 36) and (b) day 7 (n = 35) (mean ± standard error, n = 36).

Discussion

The aim of this study was to validate a reproducible model of itch induction for further pharmacological studies. Prick tests with histamine chloride and codeine phosphate on the forearms of healthy test subjects show significant and coherent variations of VAS scores with time and very significant differences with controls. A similar study also used the prick tests to compare the effects of loratadine and montelukast. The authors found similar results 10 or 15 min after the application of histamine and codeine (12).

However, differences between days 0 and 7 suggest that these tests are not reproducible in the same subjects over this time span. This could be due to the memory of induced itch that subjects acquired, which may diminish certain emotional factors, such as anxiety in comparison with the first prick tests. In the future, studies for screening anti-pruritic agents with this model should be made with only one visit or by using a ratio of scores if there are 2 visits. The main parameter for evaluating efficacy of an anti-pruritic agent should be the intensity of itch perceived 4 min after itch induction.

The development of histamine tachyphylaxis was demonstrated previously in healthy human skin and in uraemic patients (13). After repeated histamine injections at intervals of 90 min, both itch and flare responses decreased rapidly. A similar decline in histamine reactivity occurred when the interval between injections was extended to 24 h. Our study suggests that tachyphylaxis could be observed after 7 days.

Prick tests with histamine and codeine are usually positive controls for the induction of wheal and flare in allergic tests (14). Prick tests with histamine produce more itch than iontophoresis, which induce rather transient itch sensations (15). Flare reactions are correlated with itch VAS scores, but wheal is not, which suggests that this is an independent phenomenon (15). Intersubject variations of wheal size are lower with histamine than with codeine (16). However, we did not find such results with our tests. It is notable that all tested subjects were young adults. A new study with different age groups could be interesting.

Codeine induces release of histamine and tryptase by activating mast cells, as confirmed by microdialysis (17), but naloxone does not attenuate these effects. It is unlikely that μ-opioid receptors are involved in this mast cell activation. Analogies between cough and pruritus suggest that this effect could be due to δ-opioid receptors (18, 19). Whatever the mechanism, codeine-induced itch is secondary to the release of histamine. However, this phenomenon is probably very fast because we did not find a delayed effect of codeine by comparison with histamine in our work.

Although skin prick tests with histamine and codeine are very useful to evaluate IgE-mediated allergic disorders, many variations of the techniques are described and there is a need to validate procedures and very recent studies on this topic (20). Concerning itch evaluation, we did not find such studies, with the exception of Van Neste (7), who performed a similar study with histamine (but not codeine) and did not study reproducibility.

References

1. Wahlgren CF. Measurement of itch. Sem Dermatol 1995; 14: 277–284.

2. Misery L, Cambazard F. Itch metrology. In: Agache P, Humbert P, editors. Measuring the skin. Berlin: Springer, 2004: p. 670–674.

3. Yosipovitch G, Zucker I, Boner G, Gafter U, Shapira Y, David M. A questionnaire for the assessment of pruritus: validation in uremic patients. Acta Derm Venereol 2001; 81: 108–111.

4. Majeski CJ, Johnson JA, Davison SN, Lauzon CJ. Itch Severity Scale: a self-report instrument for the measurement of pruritus severity. Br J Dermatol 2007; 156: 667–673.

5. Savin JA. How should we define itching? J Am Acad Dermatol 1998; 39: 268–269.

6. Paus R, Schmelz M, Biro T, Steinhoff M. Frontiers in pruritus research: scratching the brain for more effective itch therapy. J Clin Invest 2006; 116: 1174–1185.

7. Van Neste D. Skin response to histamine dry skin prick test: influence of duration of the skin prick on clinical parameters and on skin blood flow monitoring. J Dermatol Sci 1990; 1: 435–439.

8. Van Neste D. Skin response to histamine. Reproducibility study of the dry skin prick test method and of the evaluation of microvascular changes with laser Doppler flowmetry. Acta Derm Venereol 1991; 71: 25–28.

9. Pfab F, Valet M, Sprenger T, Toelle TR, Athanasiadis GI, Behrendt H, et al. Short-term alternating temperature enhances histamine-induced itch: a biphasic stimulus model. J Invest Dermatol 2006; 126: 2673–2678.

10. Valet M, Pfab F, Sprenger T, Woller A, Zimmer C, Behrendt H, et al. Cerebral processing of histamine-induced itch using short-term alternating temperature modulation – an FMRI study. J Invest Dermatol 2008; 128: 426–433.

11. Leknes SG, Bantick S, Willis CM, Wilkinson JD, Wise RG, Tracey I. Itch and motivation to scratch: an investigation of the central and peripheral correlates of allergen- and histamine-induced itch in humans. J Neurophysiol 2007; 97: 415–422.

12. Kupczyk M, Kuprys I, Gorski P, Kuna P. The effect of montelukast (10 mg daily) and loratadine (10 mg daily) on wheal, flare and itching reactions in skin prick tests. Pulm Pharmacol Ther 2007; 20: 85–89.

13. Ståhle-Bäckdahl M, Hägermark O, Lins LE. The sensitivity of uremic and normal human skin to histamine. Acta Derm Venereol 1988; 68: 230–235.

14. Piette V, Bourret E, Bousquet J, Demoly P. Prick tests to aeroallergens: is it possible simply to wipe the device between tests? Allergy 2002; 57: 940–942.

15. Darsow U, Ring J, Scharein E, Bromm B. Correlations between histamine-induced wheal, flare and itch. Arch Dermatol Res 1996; 288: 436–441.

16. Lin RY, Erlich ER, Don PC. Skin prick test responses to codeine, histamine and ragweed utilizing the Multitest device. Ann Allergy 1990; 65: 222–226.

17. Blunk JA, Schmelz M, Zeck S, Skov P, Likar R, Koppert W. Opioid-induced mast cell activation and vascular responses is not mediated by mu-opioid receptors: an in vivo microdialysis study in human skin. Anesth Analg 2004; 98: 364–370.

18. Misery L. Are pruritus and scratching the cough of the skin? Dermatology 2008; 216: 3–5.

19. Takahama K, Shirasaki T. Central and peripheral mechanisms of narcotic antitussives: codeine-sensitive and -resistant coughs. Cough 2007; 3: 8.

20. Scherer K, Grize L, Schindler C, Surber C, Bircher AJ. Reaction pattern to histamine and codeine in a human intradermal skin test model. Clin Exp Allergy 2007; 37: 39–46.