Swelling in a lower limb and changes in skin colour after a vaccination

After young children are administered their first injectable vaccinations, a reaction may occur that involves swelling and discolouration of the lower extremities. These are transitory symptoms. The symptoms are internationally referred to as the discoloured leg syndrome. 

This is a rare reaction. In data collected in the Netherlands, around six out of ten thousand vaccinated children were reported to have the reaction. The incidence decreased as the vaccine recipients grew older.

Symptoms of discoloured leg reaction

Symptoms are detected in either or both lower limbs and may extend to the pelvis. Symptoms include:

  • smooth or patchy redness, bluish or purple discoloration on the skin of the lower extremities
  • swelling
  • small subcutaneous haemorrhages, i.e. petechia (without a decrease in platelet count).

Symptoms may also occur individually. The child also often cries a lot.

The exact mechanism behind the symptoms is unknown. A vasomotor reaction affecting the diameter of the blood vessels has been suspected as the cause. 

The purple shade of the lower extremities may also be caused by the vaccination situation itself. When a young child cries, the pressure in the abdominal cavity increases and the blood flow in the lower extremities temporarily decreases. This results in venous blood packing to the legs, causing the purple colour of the skin.

As the symptoms occur quickly, it is easy to confuse them with an anaphylactic reaction.

Treating discoloured leg reaction

Elevate the legs and place cold wraps on the skin to cool it down.
The symptoms will usually disappear without treatment in a few hours. It naturally takes slightly longer for the haematoma to disappear. 

Follow-up vaccinations

The follow-up vaccinations can be given as normal.