Dahl’s sign which is also known as Thinker’s sign or Target sign is a clinical sign in which areas of hyperpigmentation are seen on the
skin of the lower thighs and elbows. It occurs in patients with longstanding severe chronic obstructive pulmonary disease.
The sign occurs because patients with COPD tend to sit forwards with their arms resting on their thighs, leading to chronic erythema of the
skin at the points of contact. Over time, haemosiderin released from red blood cells trapped in the skin is released causing a brown discolouration of the
Air trapping in the lungs of COPD patients causes the diaphragm to be pushed down and flattened, which reduces the effect of
contraction of the diaphragm during inspiration. Sitting forwards pushes the abdominal contents upwards, increasing the curvature of the diaphragm and
improving its effectiveness. This is why, when we attend patients in severe asthma, they are often in the tripod position.
The relevance of Dahl’s Sign to paramedics:
As paramedics we often attend patients who have COPD. Sometimes these patients may appear very short of breath, but are not able to
explain that they have COPD. Dahl’s sign is one way to identify that a patient has COPD normally. It is one clinical factor, and of course not the only thing that you should rely on in your treatment decisions for this patient.