Dahl's sign (also Thinker's sign or Target sign)[1] is a clinical sign in which areas of darkened (hyperpigmentation) and thickened (hyperkeratotic) skin are seen on the lower thighs and elbows.[2] It occurs in patients with longstanding severe chronic obstructive pulmonary disease.[3]
| Dahl's sign | |
|---|---|
| Differential diagnosis | 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 skin.[4]
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.[5]
Bilateral cubital tunnel syndrome may also be found in patients with Dahl's sign.[6]
Dahl's sign was described by K. V. Dahl in 1970.[1]
References
edit- ^ a b Pavithran K. Thinker's sign. Indian J Dermatol Venereol Leprol 1992;58:266-7. Full text Archived 2020-03-14 at the Wayback Machine
- ^ Miller, P. Elliott; Houston, Brian A. (24 July 2014). "Dahl's Sign". New England Journal of Medicine. 371 (4): 357. doi:10.1056/NEJMicm1309904. PMID 25054719.
- ^ Meegada, S; Annakula, M; Challa, T; Siddamreddy, S; Peddi, P (4 February 2020). "Dahl's Sign: An Indicator of Severe Chronic Obstructive Pulmonary Disease". Cureus. 12 (2): e6865. doi:10.7759/cureus.6865. PMC 7057244. PMID 32190435.
- ^ Grandjean, R; Huber, LC (July 2019). "Thinker's sign". Cleveland Clinic Journal of Medicine. 86 (7): 439. doi:10.3949/ccjm.86a.19036. PMID 31291184.
- ^ Jeff Wiese, Stephen Bent, Sanjay Saint. Clinical Clerkships, page 252. Lippincott, Williams & Wilkins, 2005. ISBN 978-0-7817-3754-8.
- ^ Dale Berg, Katherine Worzala. Atlas of adult physical diagnosis, page 365. Lippincott, Williams & Wilkins, 2006. ISBN 978-0-7817-4190-3.