Comprehensive Overview of Nail Anatomy, Disorders, Systemic Signs, and Treatments

Conclusions

• Nail findings can be a valuable diagnostic window into systemic disease, so clinicians should routinely examine all 20 nails and not treat nail changes as isolated cosmetic problems.
• Different nail abnormalities tend to localize to specific parts of the nail unit, and matching the pattern to the anatomy helps guide diagnosis and biopsy site selection.
• Many common nail disorders are caused by trauma, wet work, inflammation, infection, medications, or systemic illness, so the differential diagnosis must be broad.
• Onycholysis, onychoschizia, onychorrhexis, onychomadesis, pitting, Beau’s lines, splinter hemorrhages, and other classic signs can each point to distinct underlying processes.
• Certain nail patterns should trigger screening for important systemic conditions such as psoriasis with psoriatic arthritis, thyroid disease, anemia, liver disease, renal disease, pulmonary disease, and malignancy.
• Red lunula or COVID-like toe/nail changes may be clues to SARS-CoV-2 infection, while splinter hemorrhages or Beau’s lines in multiple nails should raise concern for systemic disease or drug effects.
• Yellow nail syndrome is a rare multisystem disorder that is best recognized by yellow, slow-growing nails plus lymphatic or respiratory disease, and it often responds best to vitamin E combined with an azole antifungal.
• Onychomycosis has recognizable dermoscopic patterns, but diagnosis still requires mycologic confirmation, especially because nail fungus can mimic or coexist with other disorders.
• Efinaconazole and other antifungals can be effective for onychomycosis in older adults, but improvement is slow because nail growth is slow.
• Cancer therapies, especially EGFR inhibitors and other targeted or cytotoxic agents, commonly cause nail toxicity such as onycholysis, Beau’s lines, paronychia, and hemorrhages, and these effects should be anticipated and managed supportively.
• Nail lichen planus is uncommon but potentially scarring, so early recognition and timely treatment are important to prevent permanent nail damage such as dorsal pterygium.
• More aggressive treatment is warranted for severe or matrix-involving nail lichen planus, while limited disease may respond to intralesional corticosteroids and other local therapies.
• Emerging treatments such as JAK inhibitors, platelet-rich plasma, and possibly minoxidil may improve some inflammatory or dystrophic nail disorders, but much of the evidence remains case-based or early.
• Intralesional nail injections can be useful for selected nail diseases when performed carefully, with a thin needle, slow technique, patient coaching, and attention to the correct anatomic target.