Revisiting the origin, evolution and morphological nuances o
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The “butterfly sign” was described by Telfer Reynolds, MD, a hepatologist, in the Annals of Internal medicine in 1973 after observing a butterfly-shaped sparing of the skin on the back of a patient of primary biliary cirrhosis with generalized pruritus and hyperpigmentation.[1] A total of 81% of his patients with “chronic jaundice” had pruritus and 70% of those showed the “butterfly sign”.

Therefore, it can be concluded that the butterfly sign was described by him to depict frequent sparing of an area over the upper back from pigmentation where the patient cannot easily reach to scratch. It also indicated the effect of skin irritation induced by the act of scratching that produced a melanosis in what he described as patients with “chronic jaundice.”

Majority of these patients had primary biliary cirrhosis and the rest had cholangitis or bile duct cancer, conditions where intense generalized itching is often encountered, unlike in patients with liver parenchymal disease or those with congenital abnormalities of bilirubin excretion. One patient had CREST syndrome (calcinosis cutis, Raynaud's phenomenon, esophagial dysmotility, sclerodactyly, and telangiectasias) with primary biliary cirrhosis and severe arthritis making it difficult for her to scratch her back. Ten years later “the butterfly sign” was described in dermatology literature by Goldman et al. with one dark-skinned patient of chronic obstructive hepatobiliary disease.

They opined that the pigmentation secondary to the scratching was essentially a post-inflammatory hyperpigmentation (PIH) and the butterfly-shaped apparent “hypopigmentation” was actually a result of pigmentary contrast owing to the area not being accessible to scratching with hands. The article further mentions that such PIH and the sparing sign could also accompany generalized pruritus originating from renal, endocrine diseases and malignant neoplasms like Hodgkin's lymphoma.

Kimura and Miyazawa used the “butterfly sign” validating the fact that atopic dermatitis (AD) is “an itch that rashes”. They examined the back of patients with varied presentations of AD and observed that the exact shape of a butterfly did not always exist in the “butterfly sign” and described two of their cases with “umbrella sign” and “balloon sign”. They attributed the variations of the butterfly sign to the type of the skin lesions present, the ability of the patient to reach the upper part of the back, and the enthusiasm of scratching.

The eponymous “Butterfly sign” is an example of a “sparing phenomenon” of which there are many. It denotes an area of normal or relatively hypopigmented skin owing to its inaccessibility to being scratched by patients of generalized pruritus. The sign has been described in cases of hepatobiliary disorders atopic dermatitis in Japanese patients, prurigo nodularis, Vagabond's disease, and acne excoree.

It is likely to be seen in other diseases presenting with generalized pruritus of non-inflamed as well as inflamed skin. Intensity of itch, irritation, the resultant degrees of hyperpigmentation, and/or lichenification in areas surrounding the spared area makes it easier to appreciate the “butterfly sign”. It is probably more common in persons with dark skin owing to their higher tendency to develop PIH. The originally described “butterfly sign” was described over the spinal column and limited areas lateral to it, the two being analogous to the central thorax, abdomen, and wings of the butterfly. However, in a large number of patients the “butterfly sign” does not resemble a butterfly and is of varying shapes.

Such examples have led to the introduction of new signs based on anecdotal, even single cases, like the “umbrella sign” and “balloon sign” that serve a limited purpose. Such variably shaped areas of sparing are in fact, examples of “butterfly sign sine butterfly” Observation, and description of morphology have been integral parts of dermatology and it is out of these that eponymous signs are born. Revisiting them from time to time enables the clinician to appreciate their variations and evolution. Finally, ensuring accuracy in describing observations and seeing an adequate number of cases before introducing eponymous signs appears vital in the opinion of the author.