Achenbach syndrome (a.k.a. paroxysmal finger hematoma and ‘blue finger’ syndrome ) is a benign condition which features spontaneous episodic pain and swelling in the joints of one or more fingers, along with the subsequent appearance of a bruise on the palm side of the affected finger joints.

The first recorded description of this syndrome dates back to 1958 when the German doctor Walter Achenbach reported a condition that he called ‘paroxysmal hand hematoma’ or ‘finger apoplexy’. In his original work, he presented six cases of women who had experienced recurrent attacks of acute onset pain on the palmar side of one or more digits, followed by blue discoloration."

Source : Vascular Medicine, Volume 24, Issue 4

The specific cause of the condition is unknown, though it's presumed to involve small-scale spontaneous bleeding from minor veins around or near the joints. It usually self-resolves, without any permanent damage, in a few days or weeks.

It's often mis-diagnosed as other more problematic diseases such as Acrocyanosisplugin-autotooltip__plain plugin-autotooltip_bigAcrocyanosis

Acrocyanosis is persistent blue-ish discolouration of the extremities, most commonly in the hands, feet, nose and ears - sometimes with a cold and sweaty feel to the skin. In the benign form (called Primary Acrocyanosis) which is the most common, there are no other symptoms: and usually no pain, and no loss of function. or Raynaud's syndromeplugin-autotooltip__plain plugin-autotooltip_bigRaynaud's syndrome

Raynaud's syndrome, first described in 1862, is a relatively common medical condition in which extreme vaso-constriction of the peripheral blood vessels leads to reduced blood flow in the minor arteries of the fingers and toes, and in some cases the nose, ears, or lips., leading to stress for patients and unnecessary inappropriate treatments.