Pediatrics
Age changes everything
The same presentation at four ages, side by side, so the differential and the workup move with the age rather than living in one list. Each topic ends with one committed question.
Fever
The younger the child, the less reliable the examination and the higher the chance that a fever without a source is a serious bacterial infection.
Vomiting
Vomiting is a symptom of the whole child: in the newborn it may be obstruction, in the infant a surgical abdomen or a metabolic disease, in the older child a head, a gut or a ketone problem.
Cough and difficulty breathing
Airway calibre, the viruses that circulate, and the diseases that present change with age; the phrase 'difficulty breathing' means bronchiolitis in an infant and asthma in a schoolchild.
Abdominal pain
The surgical causes of a painful abdomen are almost entirely age-specific, and young children localize pain poorly, so age is the first clue to where to look.
Limp
The hip pathologies of childhood are stacked by age: developmental dysplasia in the infant, transient synovitis and septic arthritis in the small child, Perthes in the school-aged, slipped upper femoral epiphysis in the adolescent.
Jaundice
In the newborn, jaundice is a bilirubin-and-time question with a treatment threshold; in the older child it is a liver question.
Headache
Young children cannot describe a headache, so the red flags are behaviour, growth of the head, and the neurological examination; in the older child the history does the work.