"Toggle Test" in Dermoscopy of Papulo-Squamous Lesions: An Essential Step for Holistic Evaluation.

Dermatosocpy has come of age with specific signs having been described for most of the dermatoses. There have been rapid technological advancements in the equipment used. However, with an improvement in technology, previous landmarks are quickly forgotten. For example, with the advent of polarised light, the non-polarised dermoscopy findings took a back seat. The clarity of images and depth of visualisation achieved by polarisation lead to most of the signs being described and most of the examination being done in this mode. This is to the extent that unless otherwise specified, dermatoscopy refers to polarised light dermatoscopy. We believe that this results in an incomplete evaluation of a skin lesion.

For most dermoscopes, “toggling” is possible between non-polarised and polarised modes. It should be routinely used, especially for papulo-squamous lesions and many other lesions with surface features. “Toggle test”, i.e., examining the same lesion first with non-polarised mode and then with polarised mode, while maintaining the same position gives holistic information; as non-polarised view shows surface features (pattern of scale, follicular plugs, comedones, etc.) while polarised view reveals sub-surface features (erythema, telangiectsiae, vascular patterns, pigment distribution, etc.). A combination of these two findings can thus help differentiate between several clinical confounders.

We have found “toggle test” to be useful in lichen nitidus (non-polarising view shows radial ridges in “sunburst pattern”; while polarising view shows ill-defined hypopigmentation with diffuse erythema).[1] For close clinical differentials like follicular eczema, non-polarising view shows folliculo-centric scale and loss of dermatoglyphics; while polarising shows irregularly arranged folliculo-centric dotted, irregular linear, and tortuous vessels [Figure 1a and b]. In frictional lichenoid dermatitis, the non-polarising view shows superficial scaling in a ringed pattern; while polarising enhances the scale, without any discernible vessels [Figure 2a and b]. There are numerous other clinical applications possible, suggesting that “toggle test” should be done for skin lesions, by examining the same lesion with and without polarisation to holistically report upon the findings.

Figure 1

(a and b) A patient with follicular eczema shows folliculo-centric scale and loss of dermatoglyphics (a: non-polarising view) and irregularly arranged folliculo-centric dotted, linear and tortuous vessels (b: polarising view) [Dinolite AM7115MZT; 70X]

Figure 2

(a and b) Another patient with frictional lichenoid dermatitis shows superficial scaling in a ringed pattern (a: non-polarising) and an enhanced scale, without any discernible vessels (b: polarising view) [Dinolite AM7115MZT; 50X]

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