can this be a solution

Code:
SELECT DISTINCT pd1.Firstname, pd1.Lastname, pd1.Diagnosis_location, Medical_record_number
FROM patientdata pd1 JOIN patientdata pd2
USING(Medical_record_number)
WHERE pd1.Firstname = pd2.Firstname
    AND pd1.Lastname = pd2.Lastname
    AND pd1.Date_of_Birth = pd2.Date_of_Birth
    AND pd1.Diagnosis_location != pd2.Diagnosis_location
ORDER BY pd1.Lastname;