Short stature and poor linear growth — formative SAQs

SAQ 1 (10)

A 6-year-old boy is referred because he is the smallest in his class. His height is at the 3rd centile and has tracked parallel to that centile over 18 months. Both parents are short. Examination is normal, with a normal upper-to-lower segment ratio. Bone age matches chronological age. [2]

1. Define short stature and state why growth velocity matters more than a single measurement. (3) [2] [5]
2. List four features that support a normal variant (familial short stature) rather than pathological short stature. (4) [2]
3. Outline how you would calculate the mid-parental (target) height and interpret the result. (3) [6]

Model answer

Definition and velocity. Short stature is height more than two standard deviations below the mean for age and sex (about the 3rd centile). Growth velocity — the rate of change over serial measurements — matters more than a single point because a child tracking a low parallel channel is usually a healthy variant, whereas downward centile crossing is pathology until proven otherwise. [2] [5]

Familial short stature features. Short parents with a mid-parental height consistent with the current channel; normal height velocity tracking parallel to the centiles; normal examination including a normal upper-to-lower segment ratio and normal puberty; and a bone age that matches chronological age. Together these support a normal variant rather than disease. [2]

Mid-parental height. Using the Tanner approach, the target for a boy is the average of the parental heights plus 6.5 cm, and for a girl the average minus 6.5 cm, with a corridor of about ±10 cm. The child is expected to track within this corridor; a height far below it warrants investigation even if the centile looks normal. The formula is imprecise at the extremes, so use it as a corridor rather than a prediction. [6]

SAQ 2 (10)

An 8-year-old girl has crossed from the 25th to below the 3rd height centile over two years. Her weight has risen. She is tired and constipated, and there is a small goitre. [2]

1. What growth pattern is this, and what does the weight-versus-height relationship suggest? (3) [2] [4]
2. List the directed first-line investigations you would order, with a reason for each. (4) [2] [4]
3. State when idiopathic short stature is an appropriate label. (3) [1] [5]

Model answer

Pattern and weight-versus-height. This is growth failure — downward centile crossing — which is pathological until proven otherwise. Weight rising while height falls points toward endocrine disease, and the tiredness, constipation and goitre make acquired hypothyroidism the leading diagnosis. This contrasts with acute energy deficit, which drops weight before height. [2] [4]

Directed first-line tests. Thyroid function (TSH and free T4) to confirm or exclude hypothyroidism; coeliac serology to pick up coeliac disease presenting as short stature before gut symptoms; full blood count and inflammatory markers for chronic disease or anaemia; electrolytes, renal and liver function for chronic systemic disease; and IGF-1 with IGFBP-3 as a screen of the growth-hormone axis. Bone age assesses growth tempo. The pattern here, not a fixed mega-panel, guides the choice. [2] [4]

Idiopathic short stature. Idiopathic short stature is a residual label for height below −2 SDS after a complete evaluation — excluding systemic, endocrine and genetic causes and with normal stimulated growth-hormone testing under consensus criteria. It is reached at the end of the work-up, never assigned at a first glance to a child near the 3rd centile. [1] [5]