Fatigue and lethargy in children and adolescents

A parent says their child is “always tired.” That sentence can mean three different problems. The first is ordinary sleep debt after late nights and early school. The second is medical energy failure — anaemia, heart or lung disease, infection, endocrine disease, or evolving malignancy. The third is a chronic multi-domain fatigue pattern, sometimes after infection, where activity is followed by a delayed crash. Your job is to sort these without missing the child who looks quiet because they are seriously ill. [1] [5] [6]

Sister pages own deep disease algorithms: recognising the seriously ill child, pallor and anaemia pathways, weight-loss work-up, and sleep or mental-health leaves. This page owns the presentation logic for fatigue and lethargy. [8] [13]

Overview & Definition

Picture two children in the waiting room. One school-age child sits up, answers questions, and says they feel wiped after late gaming. Another infant lies still, barely tracks your face, and the parent says “this is not my baby.” Both may be labelled “tired” by a triage note. Only one is using emergency language. [8] [14]

Fatigue means reduced energy or stamina with preserved interaction. The child can still engage, though they may stop sport or need more rest. Lethargy means reduced responsiveness or spontaneous activity that worries a clinician. In infants and young children, lethargy sits next to altered consciousness. Treat it as a threat until you prove otherwise. [8] [15]

Chronic labels such as myalgic encephalomyelitis / chronic fatigue syndrome (ME/CFS) are clinical diagnoses made after a careful process. They are not a bin for every unexplained tired child on day three of a viral illness. Severe paediatric ME/CFS is uncommon but highly disabling when present, as British Paediatric Surveillance Unit work shows. [2] [3] [2]

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