What causes koilonychias?

What Causes Koilonychia?

Koilonychia (spoon-shaped nails) is most commonly caused by iron deficiency, whether with or without anemia, and should prompt evaluation of iron stores and investigation for underlying causes of iron depletion. 1

Primary Causes

Iron Deficiency

• Iron deficiency is the classic and most important systemic cause of koilonychia, manifesting as a specific sign of depleted iron stores 1
• Iron deficiency anemia affects over 1.2 billion people worldwide and is particularly common in children and reproductive-age women 2
• The nail dystrophy develops due to inadequate iron for keratin synthesis in the nail matrix 3
• Koilonychia may appear even before anemia develops, making it a sensitive clinical marker 1

Dermatologic Conditions

• Inflammatory dermatoses are frequent dermatologic causes, particularly psoriasis and lichen planus, which directly affect the nail matrix and bed 3
• Onychomycosis (fungal nail infection) can produce koilonychia through chronic nail plate damage 3

Occupational and Traumatic Causes

• Chronic mechanical trauma from repetitive manual labor or farming is a significant acquired cause 4
• A study of Ladakhi highlanders found 47.16% prevalence of koilonychia, with soldiers (69.57%) and peasants/laborers (64.26%) most affected due to combined chronic hypoxia and mechanical trauma 4
• Occupational exposure causing repeated nail trauma leads to thinning of the nail plate and atrophy of the distal nail bed 4

Secondary and Rare Causes

Nutritional and Metabolic

• Plummer-Vinson Syndrome (iron deficiency with dysphagia and esophageal webs) classically presents with koilonychia 3
• Other nutritional deficiencies beyond iron can contribute to nail dystrophy 3

Physiologic and Idiopathic

• In young children, koilonychia of the toenails is commonly transient and idiopathic, resolving spontaneously without intervention 3
• This benign variant requires no treatment but should be distinguished from pathologic causes 3

Hereditary and Syndromic

• Familial cases and syndromic associations exist, though rare 3, 5
• Genetic forms may present with additional skeletal abnormalities 5

Environmental Factors

• Chronic hypoxia at high altitude increases erythropoiesis, depleting iron stores and predisposing to koilonychia 4
• Mean hemoglobin levels may remain normal (14.17 gm%) despite koilonychia in chronic hypoxic conditions, as compensatory erythropoiesis masks iron depletion 4

Clinical Evaluation Algorithm

When evaluating koilonychia, follow this systematic approach:

1. Check iron studies first: Measure serum ferritin, transferrin saturation, and complete blood count to identify absolute iron deficiency 1, 2

2. Assess for inflammatory conditions: If iron studies are normal or equivocal, check C-reactive protein and erythrocyte sedimentation rate to evaluate for anemia of chronic disease 1

3. Examine for dermatologic disease: Look for signs of psoriasis (plaques, pitting), lichen planus (violaceous papules), or fungal infection (thickening, discoloration, friable texture) 3

4. Obtain detailed history: Specifically ask about chronic blood loss (menstruation, nosebleeds), dietary intake, NSAID use, proton pump inhibitor therapy, blood donation, and occupational exposures 1

5. Consider age-specific factors: In young children with isolated toenail koilonychia and normal iron studies, idiopathic transient koilonychia is likely and requires only observation 3

Critical Pitfalls to Avoid

• Do not assume koilonychia is benign without checking iron stores, as it may be the presenting sign of significant iron deficiency or underlying gastrointestinal blood loss 1
• In men and postmenopausal women with iron deficiency anemia and koilonychia, gastroscopy and colonoscopy should be performed to exclude gastrointestinal malignancy 1
• Normal hemoglobin does not exclude iron deficiency as the cause, particularly in chronic hypoxic states where compensatory mechanisms maintain red cell production 4
• Age, sex, hemoglobin concentration, and mean cell volume are all independent predictors of gastrointestinal cancer risk in iron deficiency anemia and must be considered in risk stratification 1