Achenbach syndrome, also known as paroxysmal finger hematoma or acute idiopathic blue finger, is a rare and benign disorder characterized by the sudden onset of blue discoloration on the ventral surface of one or more fingers. The skin discoloration is usually preceded by sharp pain, numbness, and/or itching. It can later be accompanied by edema and a cold sensation.

The most commonly affected areas are the proximal and middle phalanges of the index and middle fingers, with sparing of the fingertips. While it most frequently involves the fingers, it has also been described on the palms and toes. The condition predominately affects women between 30 and 50 years.

Achenbach syndrome usually develops spontaneously without an identifiable trigger. It can sometimes occur following minor trauma. It involves the formation of a hematoma that is generally 1-2 cm in diameter. The hematoma may expand in size and involve the palm.

Although reduced capillary resistance and vascular fragility have been proposed, the etiology remains unclear. No associating coagulation disorders or consistent abnormal radiographic findings have been implicated. The symptoms are likely secondary to the infiltration and compression effects of extravasated blood. While most cases occur without any associated findings, acrocyanosis, gastrointestinal diseases, biliary diseases, and migraine headaches have been described in some cases. However, a true pathophysiologic relationship between Achenbach syndrome and these entities has not been established.

Achenbach syndrome is a self-limiting and nonurgent condition. Complete resolution typically occurs within 4 days but can take up to 2 weeks. Recurrent episodes can occur at variable time intervals.