What condition results in a dark purplish spot under the nail plate due to a blood clot?

The condition characterized by a dark purplish spot under the nail plate due to a blood clot is indeed bruised nail beds. This condition typically arises from trauma or injury to the nail, which causes blood to accumulate under the nail plate, resulting in the characteristic discoloration. The pooling of blood creates a dark appearance, which can be quite painful depending on the extent of the injury.

Other conditions mentioned do not relate to this specific symptom. Onychorrhexis refers to abnormal brittle nails that may split or break easily but does not produce discoloration from blood underneath. Onychomycosis is a fungal infection of the nail that leads to discoloration and thickening but is not related to blood clots. Plicatured nail is a structural issue involving the nail's shape and curvature without any reference to bruising or blood accumulation. Therefore, bruised nail beds is the most accurate choice for describing this condition.