Imaging the hidden in dermatology across history

The human eye can only spot the contours of skin diseases. Despite the visibility of the skin, essential aspects of skin diseases remain hidden. On the one hand, hidden because of the limitations of the human eye. On the other hand, buried and because of this, hidden beneath the variety of structures, the diversity of patterns and the large varieties of colours.

Dermatology is observation according to a system which has been developed over the course of centuries.

Developments in pathology, immunology and molecular genetics have broadened dermatological methodology. Dermatology has also developed because of new insights into causal factors and comorbid diseases of other organs. Many new and effective treatments with few side effects have been developed, based on new insights into the pathogenesis of skin diseases.

We owe the accurate descriptions of skin diseases to Hippocrates and his pupils. They also discovered connections with internal diseases (1). For example, in the Corpus Hippocraticum, we find that watch-glass nails are connected to lung diseases.

Galenus then developed the humoral theory (2), ascribing the cause of skin diseases to an imbalance of bodily fluids.

In the Middle Ages, people were afflicted by many diseases and plagues. The humoral theory remained the principle of thinking. There was little progress in medicine and skin diseases were considered a punishment by God.

In 1735 Linnaeus published his book, the Systema Naturae. The spirit of the age was one of structured systematics: classification. A detailed classification system in plant life, classifications of diseases in medicine, clearly structured compositions in music such as the themes and variations of Johan Sebastian Bach. In his major work On Cutaneous Diseases published in 1808, Robert Willan classified diseases of the skin. For the first time, the common disease of psoriasis was described as an independent entity.

In 1858, the work of Rudolf Virchow formed a revolutionary development based on the application of light microscopy in medicine: Die Cellular Pathologie in ihrer Begründung auf physiologische und pathologische Gewebslehre. A whole new methodology of observations and descriptions of diseases on a micro level was created, leading to a new type of systematic thinking. The contours of macroscopic observation were extended into another world, to that of micromorphology, a movement which could develop quite naturally in the Romantic era. Rudolf Virchow was friends with Heinrich Schliemann, who commencing in 1871 would excavate the hidden city of Troy. The drive and courage to search for the hidden was an aspect of the spirit of the age. Much of the chamber music of Johannes Brahms was first performed in the house of the innovative surgeon Theodor Billroth, where Rudolph Virchow was a frequent guest. In his letter to Wilhelm Lübke, Billroth wrote the following: ‘It is one of the superficialities of our time to consider science and art as two antipodes. Imagination is the mother of both.’

The imagination in the Romantic era became the motor of progress: what was hidden to the eye was made visible by means of new research methods and integrated into a new type of systematic thinking.

What was hidden to the naked eye was made visible through microscopy. In the first half of the 20th century, ‘cellular pathology’ led to a fundamental innovation in dermatology with Hebra, Unna, Mac Leod and Besnier as important founders. Dermatology had a strong position in the innovation of medicine. This is not surprising since the skin is visible and it requires little effort to acquire material for micromorphological research.

Macroscopical observation by the dermatologist also developed. Observation by the human eye was refined due to new insights on a micro level. Inspired by micromorphological systematics, people started to approach skin diseases differently. A new system of describing skin diseases developed: ‘primary efflorescences’, which were described by Darier in 1928 in ‘Precis de Dermatologie’ (4).

What is hidden in observations in morphology is functionality. Innovative clinicians and researchers imagined what micromorphology means in terms of functionality. Driven by imagination, extensive physiological, immunological and molecular genetic research developed in the second half of the 20th century. Immunology has developed our understanding of immunodermatoses. Lupus vulgaris, once, a frequently occurring disease with tissueloss due to tuberculosis, appear to harbour lupus erythematodes, with immunodepositions pathognomonic for the immunodermatosis lupus erythematosus. Later the follicular hyperkeratose were recognised as hallmark of the disease. A similar development occurred for blistering diseases. The immunological classification revealed hidden hallmarks, which became visible after understanding the disease in the light of immunodermatology.

Experimental dermatology developed into a strong research field which attracted many top researchers. For what happens in the skin may be studied in vivo through research. New insights into skin diseases and starting points for new treatments followed in the last decades and will follow in the years to come. In the skin we see what we understand and we treat from what we understand.