A 9-year-old girl, with no history of pathology of interest, presented with a pruritic rash, with small papulo-erythematous lesions that in some areas became confluent, affecting the palms and soles of the feet. There was no enanthema and the patient was afebrile. As a history, the patient had been taking amoxicillin for 9 days due to LII pneumonia diagnosed at the referral hospital.

The differential diagnosis initially included: Mycoplasma pneumoniae infection, viral exanthema (probably infectious mononucleosis), drug allergy to amoxicillin and toxicoderma.

In view of the patient's clinical picture, it was decided to discontinue antibiotic treatment, an antihistamine was prescribed to calm the itching and a blood test was requested.

The results of the first analysis were: ESR 31; Hb 14.1 g/dl; Ht 41; leukocytes 8,200 (N 44.7%; L 42.1%; M 9.3%; E 3.6%); platelets 564,000; GOT 91 U/L; GPT 220 U/L; ferritin 445; IgE 25.13 U/L; RAST to amoxicillin negative; serology for Mycoplasma pneumoniae IgG and IgM negative.

After this first analysis, the possible viral aetiology, probably a mononucleosis syndrome, became stronger, and after 2 weeks a control analysis was carried out with the following results: GOT 130 U/L; GPT 363 U/L; GGT 310 U/L; alkaline phosphatase 352 U/L; ESR 8; ferritin 138; Paul Bunnell negative; hepatitis A, B and C serology negative; toxoplasma serology IgG and IgM negative; CMV serology IgG positive and IgM negative; EBV serology IgG positive and IgM negative.

At this point it was decided to repeat the analysis after one month, extending the study and ruling out the most frequent causes of transaminitis. The results were: GOT 228 U/L; GPT 483U/L; GGT 257U/L; CPK 87 U/L; alpha-1-antitrypsin 147 mg/dl; ceruloplasmin 3.23 mg/dl (22-58); plasma copper 43 mcg/dl (80-160); antinuclear antibodies, anti-DNA, anti-LKM negative; IgA antitransglutaminase negative; alpha-fetoprotein negative; brucella serology negative, parvovirus B19 serology negative.

After this analysis, the suspicion was centred on Wilson's disease. To complete the study, copper in urine was requested, with a result of 170 mcg/24 h (normal: 0-60) and a liver ultrasound scan showed mild steatosis.

With suspicion of Wilson's disease, he was sent to the paediatric hepatology unit of the referral hospital where they confirmed the diagnosis and started treatment with D-penicillamine.