How Does Tb In Children Differ From Tb In Adults

The commonest age of presentation of childhood TB disease is between 1 and 4 years. As already emphasized, young age is a risk factor for infection, for progression from infection to disease, and for spread of disease to other parts of the body, i.e. dissemination. Most children with TB are not infectious to others.

The commonest type of TB in children is smear-negative PTB. This is because cavitating TB is infrequent in children.The majority of children with PTB are too young to provide a sputum specimen for smear microscopy.Therefore an alternative method of obtaining sputum, such as gastric aspiration, is required. If alternative diagnostic methods are not available or routinely practised, the children are registered as having "smear-negative PTB", even though a smear has not been done.The next commonest type is extrapulmonary TB. Common forms of EPTB in children include: miliary TB and TB meningitis (usually in children less than 3 years of age);TB lymphadenopathy (all ages);TB effusions (pleural, pericardial and peritoneal); and spinal TB (often school-aged children) (see Chapter 5). Smear-positive PTB is usually diagnosed in children older than 6 years.The prevalence of PTB is normally low between 5 and 12 years and then increases in adolescents. In adolescents, PTB is generally like adult PTB, e.g. often with cavitation.

Pathogenesis

TB disease in children is usually primary TB. Post-primary TB may occur in adults following reactivation of dormant TB bacilli acquired in childhood. The age when a child is infected determines the pattern of primary disease. Pulmonary disease in young children is closely linked to pathology of the mediastinal nodes. This is lymphobronchial TB, which results in a wide spectrum of segmental lesions.These lesions may also be found in adults, but are unusual. Adults usually develop TB in the apices of the upper or lower lobes.Young children (i.e. less than 5 years of age) are particularly susceptible to severe forms of disseminated disease following primary infection. These severe forms include miliary TB and extrapulmonary forms of TB, e.g. meningitis.

Malnourished and HIV-infected children may develop severe PTB at any age.

T^H APPROACH TO DIAGNOSIS OF TB

The diagnosis of PTB in children is difficult. If you find the diagnosis of PTB in children easy, you are probably overdiagnosing. It is easy to overdiagnose PTB, but also easy to miss the diagnosis and presume the clinical presentation is due to malnutrition or AIDS. Carefully assess all the evidence before making the diagnosis.

The diagnosis of PTB is particularly difficult in children because, under the age of 6-8 years, children with PTB rarely cough up sputum. The readily available usual test for adults and older children with PTB is sputum smear microscopy. However, there is no such "gold standard" test for the majority of children with TB.Young children usually swallow their sputum. Gastric suction and laryngeal swabs are generally not useful unless facilities are available for M. tuberculosis culture.This means that bacteriological confirmation is usually not possible.The diagnosis of PTB in children is therefore nearly always presumptive.

The approach to diagnosis of extrapulmonary TB in children is similar to that described for adults and is outlined in Chapter 5. In some hospitals, helpful special diagnostic investigations may be available. These may include microscopy of fluid (e.g. pleural fluid, cerebrospinal fluid, ascitic fluid) and TB culture, specialized X-rays, biopsy and histology.

Clinical assessment

There are no specific features on clinical examination that can confirm that the presenting illness is due to PTB. Respiratory symptoms and disease are extremely common in childhood, particularly before 5 years of age. In most cases of suspected PTB, the child has been treated with a broad-spectrum antibiotic, with no clinical response. Always look for three important clues to TB in children:

(1) Contact with an adult or older child with smear-positive PTB.

It is usually possible to identify the source of infection.This is most often the child's mother or another female carer, such as an aunt, grandmother or older sister. They are the ones who spend most time with young children. Make sure you ask for a specific history of illness in each household contact. For example, do not just ask "does anyone in the home have TB?" but also "is anyone at home ill and what are the symptoms?" Remember that the contact may have occurred 6 months to 2 years ago. This is the usual time lapse between infection and developing symptoms of disease. Adult cases of PTB are occasionally diagnosed when a child presents with suspected TB.

(2) Failure to thrive or weight loss (growth faltering).

This is a good indicator of chronic disease in children and TB may be the cause. It is not specific and may also be due to poor nutrition, persistent or recurrent diarrhoea or HIV infection.

(3) Respiratory symptoms such as cough lasting for more than three weeks in a child who has received a course of broad-spectrum antibiotics.

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