Severe redness of the lips and mouth should be distinguished from various rash infections, viral infections, acute lymphadenitis, rheumatoid diseases and other connective tissue diseases, viral myocarditis, and rheumatoid heart disease. The differences with scarlet fever are: (1) the rash begins only on the third day after the onset of the disease; (2) the rash pattern is similar to that of measles and erythema multiforme; (3) the age of onset is infants and younger children; and (4) penicillin is not effective. The differences with juvenile rheumatoid disease are: (1) the fever period is shorter and the rash is more transient, (2) the hands and feet are hard and swollen, showing frequent plantar flushing, and (3) the rheumatoid factor is negative. The differences from exudative erythema multiforme are: (1) eyes, lips, no purulent discharge and pseudomembrane formation, and (2) rash does not include blisters and crusts. The differences from SLE are: (1) the rash is not significant on the face, (2) the total white blood cell count and platelets are generally elevated, and (3) the antinuclear antibody is negative. The age of predilection is infants and boys. There are many similarities with the symptoms of infantile nodular polyarteries, but the incidence of MCLS is more frequent, the course of the disease is shorter, and the prognosis is better. The interrelationship between the two diseases has yet to be studied. The differences with rash virus infection are: (1) flushed, dry, cracked and bleeding lips with poppy tongue, (2) hard and swollen hands and feet, often with plantar flushing and late onset of membranous peeling of finger and toe tips, (3) no edema or discharge from conjunctiva, (4) increased total white blood cell count and granulocyte percentage with leftward nuclear shift, (5) significantly increased blood sedimentation and C-reactive protein. The differences from acute lymphadenitis are: (1) the cervical lymph node enlargement and pressure pain are mild, and there is no local skin or subcutaneous tissue erythema, and (2) there is no purulent lesion. The differences from viral myocarditis are: (1) prominent coronary artery lesions, (2) characteristic hand and foot changes, and (3) persistent high fever. The differences with rheumatic myocarditis are: ① prominent coronary artery lesions, ② no meaningful heart murmur, ③ the age of onset is mainly infants and children.