To the Editor: Digital clubbing is characterized by the enlargement of the terminal segments of the fingers or toes, resulting from proliferation of connective tissue between the nail matrix and the distal phalanx1 and may be a sign of respiratory and other diseases.2 Confirming clubbing requires using instruments to determine the nail bed angles or the phalangeal depth ratio (PDR) and is not performed routinely. In 1976, Schamroth3 reported a clinical sign associated with clubbing: obliteration in clubbed fingers of the diamond-shaped window normally produced when the dorsal surfaces of the corresponding finger of each hand are opposed (Figure). The reproducibility and accuracy of this sign have not been formally tested.4,5
Validity and Reliability of the Schamroth Sign for the Diagnosis of Clubbing. JAMA. 2010;304(2):159–161. doi:10.1001/jama.2010.935
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