To the Editor.—
In the "Letters to the Editor" of the January 1970 Archives (101:117), Dr. Mark Dahl described hyperpigmentation in the suprapatellar regions of patients with "emphysema." He correctly attributed them to the instinctive assumption of a characteristic sitting posture by patients with advanced respiratory insufficiency.These hyperpigmentated areas will progress to callus formation. I described the pathogenesis of these lesions in 1963.1 It is understandable that this obscure reference to a previously undescribed, albeit trivial, clinical observation could have escaped Dr. Dahl's review. It is gratifying to realize that clinicians can learn from their own observations and are not completely dependent upon printed information.
Rothenberg HJ. THE THINKER'S SIGN. Arch Dermatol. 1970;101(4):485. doi:10.1001/archderm.1970.04000040107023