Differential Diagnosis for Black Streaks Under Fingernails

Single Most Likely Diagnosis

• Melanonychia: This condition is characterized by the appearance of black or brown streaks under the fingernails due to the deposition of melanin. It is often benign but can be associated with nail trauma, nail biting, or certain medications.

Other Likely Diagnoses

• Subungual hematoma: Blood accumulation under the nail plate can cause black streaks, usually resulting from trauma to the nail.
• Nail fungus (onychomycosis): Fungal infections can cause discoloration, including black streaks, under the nail.
• Nail biting or picking: Repeated trauma from biting or picking at the nails can lead to the appearance of black streaks.

Do Not Miss Diagnoses

• Subungual melanoma: A rare but potentially deadly form of skin cancer that can present as a black streak under the nail. Early detection is crucial for treatment.
• Endocarditis: In rare cases, black streaks under the nails can be a sign of infective endocarditis, especially if accompanied by other systemic symptoms.

Rare Diagnoses

• Addison's disease: Although rare, this condition can cause hyperpigmentation, including under the nails.
• Peutz-Jeghers syndrome: A genetic disorder that can lead to the appearance of dark blue or black macules on the skin and mucous membranes, potentially including under the nails.
• Sickle cell disease: In some cases, sickle cell disease can cause changes in nail color, including black streaks, due to vaso-occlusive crises.