A 74-year-old woman with a history of type 2 diabetes mellitus, chronic ischemic heart disease and a chronic obstructive pulmonary disease (COPD) was admitted to the emergency room with asthenia and increasing dyspnea. Physical examination showed pitting edema in both of her legs with symmetric dark and hyperkeratotic areas on the lower portion of both thighs. On the back side of her arms the same hyerkeratotic black areas were observed (Fig. 1). No pruritus was referred by the patient and neck and armpits were unaffected. Edema on both legs resolved after diuretic treatment was started, however the areas of hyperpigmentation remained unchanged, giving the diagnosis of Dahl's sign.
Dahl's sign, also known as the Thinker's sign is a skin manifestation secondary to the sustained pressure of the elbows on the epidermis of both thighs by a repeated tripod position (Fig. 2). This characteristic posture, and subsequently Dahl's sign, is naturally seen in patients experiencing chronic respiratory distress and can be understood as an indicator of the chronicity and severity of the disease.1–4 Main differential diagnosis must be done with acanthosis nigricans, an entity that typically affects patients with type 2 diabetes as in our case. However, unlike Dahl's sign, acanthosis nigricans lesions are often located on intertriginous areas.
Ethical considerations
Our work has not involved experimentation on animals. It is not a clinical trial but a descriptive case. In our work, human subjects intervene, having the informed consent of the patient, who was consulted before taking the images, agreeing to use them for educational-scientific purposes. To this end, the authors ensure that they have complied with the relevant ethical standards for publication with the informed consent of the patient.
FundingNo funding or financial support of any kind has been received for the realization of this case.
Conflict of interestNone. There is no declaration of interest on the part of any author.
