Infrared Thermography is Applicable in Differentiating the Effectiveness of Anti- Inflammatory Drugs: A Complementary Test

Aims: Images obtained by infrared thermography (IT) have potential to become a useful and low-cost tool for a wide range of biological in vivo studies, including topical inflammation models. Local temperature is one of the cardinal signs of inflammation, although it is not commonly analyzed in experimental model of inflammation. In the present study IT was used to evaluate the variation in tissue temperature, as well as the temperature response to treatment with different anti-inflammatory drugs, in an experimental model of inflammation.

Study Design: Temperature, volume and thickness of paws, histological analyses, total and differential blood cells counting were the parameters analyzed. CFA-induced paw edema was performed in rats and discrepancies between animals treated or not with anti-inflammatory drugs were analyzed.

Place and Duration of Study: Holtzman male rats from Federal University of Jequitinhonha and Mucuri Valleys (Diamantina, Brazil) were tested during 28 days.

Methodology: CFA-induced paw edema was performed in rats and discrepancies between animals treated or not with triamcinolone acetonide and diclofenac sodium were analyzed. Experimental times were: T0, before chemical induction of inflammatory process (control); and several times after induction: T1 (30 min); T2 (24 hours); T3 (48 hours); T4 (72 hours); T5 (96 hours); T6 (7 days); T7 (14 days); T8 (21 days); T9 (28 days). The measured parameters were temperature, paw volume, histological and leukometric analysis.

Results: Standard deviations (SD) presented low values (0.00 to 0.54 °C), thus demonstrating the good repeatability of the infrared thermography method. Temperature values in the paws injected with saline showed no significant difference between groups (p <0.05). There was a significant difference between the mean temperatures before induction (T0) compared to 24h (T2), 48h (T3), 72h (T4) and 96h (T5) (n=5; P<0.05 ). Paw volume values ​​were different (p<0.05) in relation to initial values ​​(T0) for groups G1 (control) and G2 (triamcinolone). For group G3 (diclofenac) there was a statistical difference in the times from T2 (24 hours) to T7 (14 days). The thickness of the paws measured showed a statistical difference (p<0.05) for all moments when compared to T0. Histological sections showed areas of inflammatory cell infiltration in all groups.

Conclusion: In the present study, the temperature variation was similar to the variation in the volume and thickness of the rats paws, and the changes in tissue temperature reinforced the findings regarding the characteristics of inflammation. Furthermore, the infrared technique was useful to demonstrate different responses to anti-inflammatory tests in this animal model of inflammation.