The Pursuit Continues: Comments on ‘Pursuit of Osler’s Sign’

Dear Editor, We read with great interest the excellent article by Djeamourthy S et al.[1] titled ‘Pursuit of Osler’s sign’. We applaud the efforts of the authors in describing the challenges in detail. However, we would like to highlight some important aspects related to alkaptonuria (AKU). The case should have undergone a few specific urinary tests for the confirmation of diagnosis, as there are several different conditions in which such ocular and urinary pigmentation can be seen. AKU like ochronosis can also be seen due to substances like phenol, hydroquinone, quinine, minocycline and methyldopa. The gold standard test for AKU is to detect homogentisic acid in the urine. Various easily available tests are as follows: Alkali test- On addition of NaOH to urine, it turns black. Ferric chloride test- transient green colour is seen. Ammoniacal silver nitrate test-forms black precipitate of silver. Benedict’s test-shows black supernatant and red brown precipitate of cuprous oxide at the bottom. N-butane test pink-brown colour is formed.[2] Black colour in fresh urine can be seen in conditions such as disseminated melanoma and Addison’s disease while in porphyria, freshly passed urine may be normal in colour and only darkens upon standing[3] as in AKU, and hence these disorders should also be ruled out. Hence, the urinary tests have a very important role. Finally, it must be clarified that the term ‘Osler’s sign’ is not specific for AKU, but is also used in pseudohypertension,[4] pretibial myxoedema[5] and some other pathologies. Financial support and sponsorship The authors have no proprietary or commercial interest in any material discussed in this article. Conflicts of interest There are no conflicts of interest.