ESPE Abstracts

Background and Aim: Achondroplasia is the most common skeletal dysplasia and is associated with serious complications such as foramen magnum stenosis (FMS). Current guidelines in Germany recommend polysomnography at 2-3 months and cranial imaging at 6-9 months of life in achondroplasia, whereas American Academy of Pediatrics recommends to evaluate every infant with achondroplasia for cranio-cervical junction risks via neurologic examination, polysomnography and neuroimaging either with computerized tomography (CT) or magnetic resonance imaging (MRI) as soon as the diagnosis is recognised. Here we present an infant with achondroplasia and FMS who presented with syndrome of inappropriate antidiuretic hormone secretion (SIADH) secondary to significant FMS and myelocompression. Our aim is to draw attention to the early presentation of a life-threatening complication of achondroplasia and to discuss the optimal timing of cranial MRI.

Case report: A 2-month-old boy with prenatally diagnosed achondroplasia was referred to our university hospital due to disordered breathing and altered consciousness. On physical examination, the patient was apathic, pale, hypotonic and hypothermic (34.8°C) and had typical features of achondroplasia. Shallow breathing with nasal flaring and suprasternal retractions and deep sighing was compatible with central apnoea, blood gas analysis revealed respiratory acidosis. The patient was intubated in our paediatric intensive care unit. Laboratory investigations revealed severe hyponatremia (114 mmol/l) and hypochloridaemia (82 mmol/l) with normal glucose and urea levels and high urinary sodium-output (131.8 mol/mol Cr). The diagnosis of SIADH was made based on low serum osmolality (237 mOsm/kg) in the presence of high urine osmolality (431 mOsm/kg) and treatment was started. An emergency CT showed a high-grade stenosis at the cranio-cervical junction, subsequent MRI demonstrated myelocompression (AFMS 4b). The patient underwent decompression surgery the next day. A prompt improvement of laboratory parameters was observed after operation with an increase in serum osmolality (290 mOsm/kg) and a decrease in urinary sodium extraction (42 mol/mol Cr). Spontaneous breathing after extubation was sufficient but only reduced spontaneous motor activity of the extremities was observed in the course, hence a high-level spinal injury can be assumed.

Conclusion: Clinicians should be aware of SIADH as a presenting sign of FMS in children with achondroplasia. Further discussion is needed regarding improved family education and timing of screening recommendations including neuroimaging especially in children who did not receive polysomnography.