What is the cause and treatment of white lines in nail beds, also known as leukonychia, in a patient with potential underlying nutritional deficiencies or systemic diseases?

White Lines in Nail Beds (Leukonychia)

Immediate Diagnostic Classification

White nail discoloration must first be classified anatomically to determine whether the problem originates from the nail plate itself (true leukonychia), the nail bed (apparent leukonychia), or surface contamination (pseudoleukonychia), as this fundamentally changes both the differential diagnosis and treatment approach. 1

Anatomical Classification System

• True leukonychia involves abnormal keratinization of the nail matrix, where the white color originates from the nail plate itself and moves distally with nail growth 1, 2
• Apparent leukonychia results from nail bed pathology, where the white color does not move with nail growth and blanches with pressure 1
• Pseudoleukonychia represents surface deposits or fungal infection affecting only the superficial nail plate 1

Morphological Patterns and Their Significance

Transverse White Lines (Mees' and Muehrcke's Lines)

• Mees' lines (true leukonychia) are single or multiple transverse white bands that move distally with nail growth, classically associated with arsenic poisoning, chemotherapy, or severe systemic illness 1, 3
• Muehrcke's lines (apparent leukonychia) are paired transverse white bands that do not move with nail growth, blanch with pressure, and indicate hypoalbuminemia (<2.2 g/dL) 1, 3

Total or Partial White Nails

• Terry's nails show white discoloration of 80% or more of the nail with a narrow pink band at the distal edge, associated with cirrhosis, congestive heart failure, and diabetes 1, 3
• Lindsay's nails (half-and-half nails) display proximal white and distal pink/brown coloration, strongly associated with chronic kidney disease 1
• Total leukonychia affecting all nails from birth suggests hereditary leukonychia totalis, inherited in autosomal dominant pattern 4

Longitudinal White Lines

• Longitudinal leukonychia appears as white streaks running from proximal to distal nail, often related to trauma or Darier disease 1, 2

Critical Differential Diagnosis

Fungal Infection (Superficial White Onychomycosis)

Do not diagnose fungal infection based on appearance alone—50% of nail dystrophy cases are non-fungal despite similar clinical presentation. 5

• Superficial white onychomycosis affects the nail surface with white, flaky discoloration that can be scraped off, most commonly caused by T. mentagrophytes 5
• The nail becomes friable and soft, unlike non-infectious leukonychia where the nail plate remains hard 5
• Mandatory laboratory confirmation requires direct microscopy with potassium hydroxide (KOH) preparation and fungal culture on Sabouraud's agar before initiating treatment 5, 6
• Calcofluor white staining significantly enhances visualization of fungal elements compared to standard KOH preparation 5, 6

Bacterial Infection (Green Nail Syndrome)

• Pseudomonas aeruginosa causes green or black discoloration, not white, but can coexist with fungal infection 5, 7
• Treatment requires keeping the area dry with topical povidone iodine 2% twice daily 6, 8

Drug-Induced Leukonychia

• Chemotherapy agents, particularly taxanes (docetaxel, paclitaxel), cause nail changes in 43.7% and 34.9% of patients respectively, though these typically present as melanonychia (dark discoloration) rather than white lines 5
• Beta-blockers can cause various nail deformities including color changes 3

Systemic Disease Markers

• Hypoalbuminemia manifests as Muehrcke's lines that blanch with pressure 1, 3
• Liver disease (cirrhosis) presents as Terry's nails 1, 3
• Chronic kidney disease shows Lindsay's half-and-half nails 1
• Severe systemic illness causes Beau's lines (transverse grooves) and may trigger Mees' lines 3

Treatment Algorithm

Step 1: Determine Anatomical Origin

• Apply pressure to the nail bed—if white color blanches, this indicates apparent leukonychia from nail bed pathology requiring systemic workup 1
• Observe if white lines move with nail growth—movement indicates true leukonychia from nail matrix abnormality 1
• Attempt to scrape the white material—if it comes off easily, consider pseudoleukonychia from surface fungal infection 1

Step 2: If Fungal Infection Suspected

Never treat without mycological confirmation, as inappropriate antifungal therapy is costly and unnecessary in 50% of cases. 5

• Obtain nail clippings from the affected area for KOH preparation and fungal culture 5, 6
• For confirmed superficial white onychomycosis, systemic antifungal therapy is required as topical agents penetrate poorly 5
• First-line treatment: Terbinafine 250 mg daily for 6 weeks (fingernails) or 12 weeks (toenails) with 88% cure rate 6
• Alternative: Itraconazole pulse therapy 200 mg twice daily for 1 week per month, 2 pulses for fingernails or 3 pulses for toenails, with 94-100% cure rates 6

Step 3: If Systemic Disease Suspected

• Order serum albumin if Muehrcke's lines are present (paired transverse bands that blanch) 1, 3
• Obtain liver function tests if Terry's nails are evident (>80% white discoloration) 1, 3
• Check renal function if Lindsay's nails are observed (half-and-half appearance) 1
• Consider heavy metal screening if Mees' lines appear after acute illness or toxin exposure 1, 3

Step 4: If Trauma-Related

• Punctate leukonychia (white spots) from minor trauma requires no treatment and grows out spontaneously 1, 2
• Recommend protective measures including daily topical emollients to cuticles and nail plate, avoiding nail manipulation, and wearing protective gloves for wet work 5, 6

Common Pitfalls to Avoid

• Do not assume white discoloration equals fungal infection—only 50% of dystrophic nails are fungal, and true/apparent leukonychia from systemic disease requires entirely different management 5
• Do not overlook systemic disease markers—Muehrcke's lines, Terry's nails, and Lindsay's nails indicate serious underlying conditions requiring immediate workup 1, 3
• Do not treat fungal infection empirically—laboratory confirmation is mandatory before initiating months-long systemic antifungal therapy 5
• Do not confuse green discoloration with white—Pseudomonas infection requires topical antiseptics, not antifungals 5, 7