The crying baby and Pyrexia of unknown origin

A distinction must be made between the baby who is said to be 'constantly crying' and has done so for a long time, from the child who is crying with an acute illness.
The usual causes for 'constant crying', other than an acute illness, arc hunger, excessive wind (due to too small a hole in the teat if bottle fed), thirst due to ovcrconccntrated feeds, evening colic (first three or four months only), boredom, the desire to be picked up, excessive heat or cold, or an itchy rash. Often no cause can be found and it is assumed that the pro­blem is one of his developing personality. An erupting tooth, untreated coeliac disease or phenylketonuria, and perhaps other metabolic defects, may also present with crying. 
When a child is brought on account of constant crying, and none of the usual causes can be found, it is important to remember that the mother may be becoming worn out, and that this is a 'pre-battering' situation. 
The sudden development of constant crying in a baby pre­viously well but now ill, may be due to otitis media, urinary tract infection, meningitis or other infection, alimentary tract obstruction, subdural effusion or torsion of a testis. 
Pyrexia of unknown origin 
When the obvious causes of fever have been eliminated, in­cluding in particular otitis media, tonsillitis, urinary tract in­fection or the onset of an acute infectious disease such as measles, infectious mononucleosis, roseola infantum or enteric fever there remain many possible diagnoses to consider. The possibility of meningitis must not be forgotten.
In the newborn, an E. coli or similar septicaemia is an im­portant condition to eliminate. Chronic dehydration, due to one of the causes of polyuria, may cause a rise of temperature. Meningococcal septicaemia may present with high fever, and later on arthritis and a few petechial haemorrhages. Tuber­culosis can usually be eliminated by a tuberculin test, but not always, for the test may be negative in miliary tuberculosis and temporarily negative in measles or other infections: choroidal tubercles can be seen in two out of three children with miliary tuberculosis, and the X-ray of the chest may help to establish the diagnosis of tuberculosis, later confirmed by stomach washings and urine examination.
A perinephric or subphrenic abscess would normally be the sequel of appendicitis. Examination of all bones for tenderness or for areas of slight local warmth with blood cultures, help to eliminate osteitis. Subacute bacterial endocarditis is usually associated with congenital heart disease, of which there arc usually signs. Fever may be a manifestation of chronic liver disease, leukaemia or malignant tumours. Prolonged unex­plained fever may precede the obvious manifestations of rheu­matoid arthritis by many months. Rarer infections to eliminate include toxocara, in which there is often cosinophilia, and tox­oplasmosis.
Fever may be a side-effect of numerous drugs. Malingering is a rare cause of elevation of the temperature. By various means, including rapid rubbing of the bulb of the thermome­ter, the unwary may be deceived. However, a normal white cell count and normal ESR help to eliminate many of the infections. Very occasionally a child has a slightly raised tem­perature, is well, and nothing abnormal is found after full investigation.