Hypertrophy of the lumbosacral nerve roots in Noonan syndrome with multiple lentigines: a case report

The patient was a 61-year-old man in whom sensorineural hearing loss were noted after birth and the presence of multiple cutaneous millet-sized lentigines were noted after about 6-year-old. He had pain in his bilateral lower extremities; 1 month later, he visited our hospital. He had no family history of neurological or cutaneous symptoms. In nerve conduction studies, the F-wave frequencies were reduced in the bilateral tibial nerves. In lumbar spine magnetic resonance imaging, the bilateral lumbosacral nerve roots showed hypertrophy. A genetic analysis revealed that he had a heterozygous single-base non-synonymous substitution in the PTPN11 gene (c.1403C>T, p.Thr468Met). This substitution is known pathogenic variant. We diagnosed the patient with Noonan syndrome with multiple lentigines. This syndrome is a RASopathy that is caused by variants in genes encoding the SHP-2 protein, which is a component of the RAS/mitogen-activated protein kinase (MAPK) signaling pathway. RASopathies should be included as differential diagnoses for spinal nerve root enlargement.