Case 3: An eight-month-old boy with failure to thrive

A full-term eight-month-old boy was admitted to hospital for evaluation of failure to thrive (FTT). After initially thriving, by six months of age his weight had dropped from the 90th to the 15th percentile. He had a four-month history of nonbloody, nonbilious emesis and a worsening feeding aversion. Stool pattern remained normal. There was no sweating or increased work of breathing with feeds. Physical examination revealed a pale, emaciated infant with little subcutaneous fat. He was alert, active and engaging. He was afebrile with stable vital signs. His weight was 6.89 kg (<3rd percentile; 69% ideal body weight) (Figure 1). His head growth was stable (25th percentile) and length was preserved (75th percentile). He had no dysmorphic features, a flat anterior fontanel and normal tone. The remainder of his examination was unremarkable. The patient's growth chart. Note the plateau in weight, resulting in the crossing of multiple percentile lines Investigations included a normal complete blood count, electrolyte levels and renal function tests. A work-up for fat, carbohydrate and protein malabsorption was negative. An upper gastrointestinal swallowing study revealed normal anatomy. Lansoprazole and domperidone were initiated for gastroesophageal reflux disease. His vomiting improved; he tolerated fortified feeds, demonstrated adequate weight gain and was discharged home with follow-up. One week later, he was readmitted with weight loss and new symptoms. A further test led to the diagnosis. Staring spells and eye deviation prompted electroencephalography and brain magnetic resonance imaging. Electroencephalography was normal, but magnetic resonance imaging revealed a large suprasellar enhancing mass, extending superiorly into the third ventricle and obstructing the foramen of Monro, resulting in moderately dilated ventricles. Metastases were present in the cerebellum and spinal cord (Figure 2). AMagnetic resonance image showing the tumour in an axial slice.BMagnetic resonance image showing the tumour in a sagittal slice. The position of the tumour is typical for diencephalic syndrome The location of this tumour, in conjunction with a pale, emaciated infant with an alert and happy affect, led to a diagnosis of diencephalic syndrome (DS). Growth hormone (GH) and cortisol levels were normal. Subsequent biopsy demonstrated a neurocytic tumour with proliferative vasculature, for which chemotherapy was initiated. Our patient's course was complicated by raised intracranial pressure requiring ventriculoperitoneal shunt insertion, and insertion of a gastrostomy tube for supplemental nutrition. Sadly, our patient's tumour proved refractory to chemotherapy, and he passed away 25 months after his diagnosis. FTT is one of the most common problems in paediatrics. It is identified when a child's weight falls below the third percentile or crosses two major percentile lines. An approach to FTT requires a detailed history and physical examination with targeted investigations. Recognition and treatment of FTT is important to prevent long-term adverse outcomes associated with malnutrition. DS, first reported in 1951, is a rare but well-described cause of FTT in infancy and childhood. Associated with tumours of the anterior hypothalamus, classic features of this syndrome include profound emaciation (despite adequate caloric intake), near absence of subcutaneous adipose tissue, hyperkinesis, and an alert and happy affect (1). DS typically presents in infancy and early childhood. A review of 72 patients with DS found that the mean age at symptom onset was 6.2 months; 86% of patients presented within the first year of life (2). There is often a considerable time lag between symptom onset and diagnosis, possibly due to the overall rarity of DS in the context of the extremely common presentation of FTT (2,3). Medical attention is usually sought on account of FTT (1,2). Despite the lack of weight gain, patients' linear growth is characteristically spared (1,2). Their head circumference is usually normal, although it may be increased secondary to hydrocephalus (2). On laboratory investigation, GH levels are often elevated (2–4). While the etiology for this is unclear, one group proposes DS as a model of partial GH resistance (3). Notably, the neurological manifestations of DS are subtle, consisting of the aforementioned behavioural features, and development is usually normal or precocious (2,3). The most common true neurological finding is nystagmus, present in 55% of cases (2). The nonspecific clinical features of DS and its variable presentation reflects the lack of understanding of its pathogenesis, and alerts the clinician to keep an open mind with respect to differential diagnoses of FTT (2–4). Gliomas are reported to account for 93% of tumours associated with DS, with astrocytomas arising from the hypothalamic and optic chiasm region being most common (2,4). Astrocytomas associated with DS are generally larger, more aggressive and occur at a younger age than astrocytomas in the absence of DS (4). The majority of patients are treated with a combination of surgery and chemotherapy, with adjunct radiotherapy when indicated (3,5). Complete surgical resection is often limited on account of potentially significant neurological and endocrine sequelae, and radiation at therapeutic doses is also associated with risks due to the immature central nervous system of young children (5). Without treatment, the mean survival time of patients with DS is approximately 12 months (2,5). Accurate figures regarding long-term survival in DS are difficult to obtain due to the rarity of this syndrome and paucity of the literature regarding DS. When evaluating a child with FTT, a systematic approach that considers a broad differential diagnosis is imperative to avoid missing rare but treatable causes. DS is a rare but important cause of FTT in an infant or young child. Classic features of DS include profound emaciation, near absence of subcutaneous adipose tissue, hyperkinesis, and an alert and happy affect, associated with anterior hypothalamic tumours. Neurological symptoms that would typically prompt neuroimaging can be subtle.

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