Noonan syndrome management and follow-up

A chronic, mutlidisciplinary, system-based approach is recommended in the management and follow-up of patients with Noonan syndrome with special emphasis on the cardiac complications, growth delay, and neurocognitive deficits.

A mutlidisciplinary team is often needed in the management of Noonan syndrome. A system-based approach is usually adopted and recommendations are based on the severity of disease manifestations.

• Patients with Noonan syndrome require lifetime cardiac follow-up. After initial evaluation including a focused cardiac physical exam, echocardiography, and electrocardiography, follow up is based on work-up findings. If initial work-up is unremarkable, a follow up is recommended every 5 years. ^[1][2]

• The most common cardiac finding is pulmonary valve stenosis. If mild, only periodic follow-up is recommended. If clinically significant, pulmonary balloon valvuloplasty is recommended in the absence of significant valve dysplasia. With significantly dysplastic valves a pulmonary valvectomy or pulmonary valve homograft during childhood is the first line management. ^[3]

• The second most common cardiac manifestation of Noonan syndrome is hypertrophic cardiomyopathy. Management is usually similar to most patients with HCM and includes beta-blockers and surgical myomectomy in certain cases with significant outflow obstruction. ^[3]

• Up to 70% of patients with Noonan syndrome have some form of growth delay with mean delay in bone age of 2 years. Although growth hormone supplementation has only been studied in small studies, data suggests improved growth without significant side effects.
• Most studies with long-term follow up suggest that better outcomes are associated with earlier initiation of GH and a longer duration of treatment.^[3]
• The largest study involving 65 patients with a mean age at initiation of 11.6 years showed a mean growth of 10.9 cm in boys vs. 9.2 cm in girls with a mean treatment duration of 5.6 years at a dose of 0.33 mg/kg/week.^[4] In general, doses used in most studies ranged from 0.24-0.35 mg/kg/week.^[3]
• Special growth curves for Noonan syndrome have been developed and should be used in plotting growth.^[5]
• Plotting growth on curves specific for Noonan syndrome is recommended to be done 3 times yearly from birth till age 3 years than yearly after that.^[1]
• Patients with growth deceleration, signs of hypothyroidism, or delayed puberty should be referred to a pediatric endocrinologist.^[3]

• 10% of patients with Noonan syndrome have associated renal abnormalities. Renal ultrasound is recommended at diagnosis.^[3]
• Prophylactic antibiotics can be used for hydronephrosis or recurrent urinary tract infection.^[3]
• Cryptorchidism can be found in up to 80% of boys with Noonan syndrome and close attention to descended testes is recommended. Surgical orchiopexy is usually required by the age of 1 year.^[1][2]

• Bleeding disorders can be seen in up to 65% of patients with Noonan syndrome.^[3] An initial work-up consisting of a complete blood cell count with differential, prothrombin time and activated partial thromboplastin time is recommended.^[1]

• A repeat evaluation is required if the patient was aged 6-12 months during first screening.^[1]

• If the patient requires any surgical procedure, a pre-operative screen with added factor IX, XI, and XII concentration assays, von Willebrand factor, and platelet aggregation testing is recommended in conjunction with a hematology consult.^[1]

• Neurologic, behavioral and cognitive abnormalities are often seen in patients with Noonan syndrome although they are poorly understood and very variable among patients.^[3]

• Yearly developmental screening is recommended especially between the ages of 5 and 18 years old with individual educational plans recommended in patients with delays.^[1]

• A complete neuropsychological examination is recommended if any deficits are detected on developmental screening.^[3]

Any patient with Noonan syndrome with recurrent vomiting or feeding difficulties requires a pediatric gastroenterology consultation for further investigation and management including antireflux medications, feeding tube insertion, and surgical consult in certain cases with malrotation. ^[3]

• A complete ophthalmologic examination is recommended at diagnosis and at least every 2 years thereafter if no problems are detected.

• A hearing test in recommended during infancy with yearly retesting in early childhood, and careful attention and management of ear infections to avoid hearing loss. ^[3]

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