Subungual hematoma is caused by bleeding under the nail, most often as a result of trauma to the digit.
The trauma may be a direct blow, blunt trauma, or a crush injury to the distal phalanx.
Toenails are affected more often than fingernails.
The great toe is most often affected in tennis players, the second and third toes in squash and soccer players, and the fifth toe in joggers.
Subungual hematoma causes include: the use of medications, anticoagulants, chemotherapeutic agents, ganciclovir, and systemic diseases of diabetes, systemic lupus erythematosus.
Initially subungual hematomas are extremely painful and appear red-purple to purple-black.
Over time, subungual hematomas
become less painful, and the color changes to black, dark blue, purple, blue, or yellow-green due to breakdown of hemosiderin, and its border may become blurry.
Subungual hematomas migrate distally with the growth of the nail.
Wwhereas most of the other causes of melanonychia and pigmented lesions of the nail matrix or nail bed will remain stationary.
Transillumination of the nail combined with dermoscopy can increase diagnostic accuracy.
Subungual hematomas of usually less than 48 hours in onset can be successfully treated with simple trephination with immediate relief of pain.