Muehrcke lines in nails are seen in:

Muehrcke's lines are white lines (leukonychia) that extend all the way across the nail and lie parallel to the lunula. Muehrcke's lines - associated with decreased protein synthesis, which occur during metabolic stress & in hypoalbuminemic states such as the nephrotic syndrome. It should not be confused with Half-and-half nail syndrome/Lindsay's nails- most characteristic onychopathy seen in chronic renal failure.