Table 2.

Transverse leukonychia

True leukonychia
Traumatic	Repeated trauma to the matrix by pressure on the free edge of the nail plate when the nail is not cut short [4, 38, 39], picking away chipped nail polish [40]
Hematologic disorder	Acute myeloid leukemia [41], Hodgkin’s disease, sickle cell anemia
Neurovascular disorder	Spinal cord injury [42], epilepsy [22]
Skin disease	Psoriasis [18], acrodermatitis continua of Hallopeau [18], infection of proximal nail fold, erythema multiforme [43], pellagra [44]
Toxic	Arsenic (Mees’ lines) [35, 45–50], strontium-contaminated water [51], thallium [52, 53] Direct contact with the nail unit: herbicides: paraquat [54, 55], diquat [54, 56], dinitro-orthocresol [57]
Drugs	Ciclosporine [58], cytostatics (many) [59, 60], synthetic opioid MT-45 [61], retinoids (acitretin, etretinate, isotretinoin) [62–64], sulfonamide [65], pilocarpine [65]
Hormonal	Menstrual cycle [66]
Infectious	Bacterial: pleural empyema [67, 68], acute pulmonary tuberculosis in human immunodeficiency virus [68] Viral: COVID-19 [69, 70], Kawasaki disease [71], herpes zoster [72] Parasitic [73]
Systemic disease	Systemic lupus erythematosus [74], chronic kidney disease [75, 76], acute rejection of a renal allograft [77], congestive heart failure [78]
Environmental	High altitude [79–81]
Apparent leukonychia	(Muehrcke’s lines)
Systemic diseases	Hypoalbuminemia [82, 83], kidney transplants [84], patients with chronic renal failure undergoing hemodialysis [76], active rheumatoid arthritis [85], heart transplantation [86, 87], left ventricular assist device [88]
Drugs	Retinoids: acitretin [89], transretinoic acid [90] Cytostatics: cyclophosphamide, adriamycin, and vincristine [91], 5-fluorouracil plus leucovorin [92], cyclophosphamide/doxorubicin/5-fluorouracil [93], 5-fluorouracil/adriamycin/cyclophosphamide [94]
Pseudoleukonychia
Skin disease	Onycholysis Proximal subungual onychomycosis [30, 33, 95], white superficial onychomycosis [30]