Kawasaki disease (KD) is a febrile vasculitis that affects children under five. Ptosis and muscle weakness are uncommon side effects of KD. There was a case where a 3-year-old boy with KD, eyelid ptosis, and muscle weakness were presented. Grade IV and grade III muscle strength were measured in the upper and lower limbs, respectively, at admission. The patellar tendon reflex was found to be diminished. With a serum potassium value of 2.62 mmol/L, laboratory testing revealed hypokalemia. Intravenous immunoglobulin (IVIG) and aspirin were started right away, along with methylprednisolone as a supplement.

Potassium supplementation was given simultaneously, which corrected hypokalemia on the second day of admission but did not alleviate ptosis or muscle weakness. Researchers conducted Neostigmine testing, lumbar puncture, electromyography, and cerebral and complete spine MRI, but they did not find any neurological or muscle illnesses. The fever subsided on the fifth day. Eyelid ptosis was gone by the sixth day. They restored muscular strength and tension to normal on the 14th day, the patellar tendon reflex could be drawn out regularly, and the youngster regained full ambulatory capacity. The neurological and muscular systems may be affected by KD, and KD, worsened by eyelid ptosis, and muscle weakness responds to standard anti-inflammatory treatment plus supplementary corticosteroid therapy.