normal nail. Named after the American nephrologist who first described them in 1956, ML usually involve
the second, third, and fourth fingers. They reflect a vascular abnormality in the nail bed (typically,
subungual edema), and not in the nail plate. Hence, they do not progress distally with nail growth.
Common in hypoalbuminemia (<2.2 gm/100 mL), they disappear with its resolution. In his original study,
Muehrcke found paired, transverse, white bands in 23/31 (74%) patients with nephrotic syndrome and 8/9
with hypoalbuminemia (<2.3 gm/100 mL) from other causes.
Lines were instead absent in all healthy subjects, and in those with albumin >2.2 gm/100 mL. Bands were more prominent after albumin had been <1.8 gm/100 mL for at least 4 months. In another study by Conn and Smith, Muehrcke lines were seen in 10/44 (23%) patients with hypoalbuminemia from various debilitating illnesses, but absent in those with normal serum levels. Hence, ML occurs in hypoalbuminemia from many reasons, including nephrotic syndrome, but also liver disease and malnutrition. Additionally, they can occur in pellagra, Hodgkin’s disease, sickle cell anemia, or nail damage from paraquat and chemotherapeutic agents.
Although transverse white bands in the nail plate are often due to trauma to the matrix at the proximal nail fold (leukonychia), Muehrcke’s (and Mees’) lines are instead associated with a systemic disease. They
typically span the entire breadth of the nail bed/plate, tend to be more homogenous, have a contour similar to the distal lunula (with a rounded distal edge and smoother borders), occur on several nails at once, and
typically follow a generalized insult. Trauma-induced transverse white bands tend to be more linear, do not
spread across the entire breadth of the nail plate, resemble the contour of the proximal nail fold (where
trauma occurred), and have a history of localized trauma to the cuticle.