Objective: To demonstrate use of muscle ultrasound (MUS) in the diagnostic evaluation of pediatric neuromuscular disorders through a case report of a patient with INPP5K-related muscular dystrophy
Background: Biallelic pathogenic variants in INPP5K have been associated with a rare form of congenital muscular dystrophy (MD) that presents with muscular weakness, short stature, intellectual disability, as well as additional features of epilepsy, cataracts, and cerebellar atrophy. Characteristic muscle involvement has been identified on muscle MRI in a small case series, including consistent involvement of the vasti, anterior tibialis, and peronei with relative sparing of the rectus femoris, sartorius, and gracilis. MUS may also be a helpful clinical tool to screen for neurogenic versus myopathic disease processes and specific muscle involvement.
Results: A now 3-year-old girl was initially evaluated for failure to thrive with small stature and motor delays. Over time she was found to have elevated CK in the 1000s and developed a cataract. She had initial non-diagnostic genetic evaluation with chromosomal microarray and congenital myopathy gene panel. She subsequently underwent muscle biopsy, which showed myopathic changes, followed by exome sequencing that revealed a likely pathogenic variant (c.1229_1230delTT) and a variant of uncertain significance (c.553G>T) in the INPP5K gene. Parental testing confirmed the variants to be in-trans. Given the compelling variants and clinical fit, she was diagnosed with INPP5K-related MD. MUS completed after diagnosis was further supportive, as characteristic features were seen including relative sparing of the rectus femoris.
Conclusions: This case highlights the use of MUS as a clinical tool. MUS may be particularly helpful with identifying recognizable patterns that may help phenotyping of genetic neuromuscular disorders. MUS also has the advantage of being able to be done quickly at the bedside and without sedation, and thus can be easily used as an extension of the pediatric neuromuscular exam.