Case 2: Hypotonia and Muscle Weakness since Birth in a 2-year-old Boy

Presentation

A 2-year-old boy presents to our clinic with hypotonia and muscle weakness since birth. He has motor developmental delay: he has never crawled because he has had difficulty lifting his head. His mother denies any dysphagia, difficulty breathing, or seizures and reports that he can walk for only 1 to 2 minutes and fatigues easily. His symptoms are nonprogressive and improve on rest.

He was born at 37 weeks' gestation by cesarean delivery. His mother received good prenatal care. He was found to be hypotonic at birth, although his mother did not report any reduced fetal movements. He stayed in the NICU for 4 days for feeding difficulty and oxygen requirement. A cranial computed tomographic (CT) scan was normal at that time. There was no family history of any muscle weakness.

During this visit, he is smiling and comfortable. He is at the 30th percentile for height and the 45th percentile for weight, with normal vital signs. On examination he has diffuse muscle wasting, including face and symmetrical weakness of all 4 extremities, along with a positive Gower sign and ptosis. He has postural scoliosis and a waddling gait. His reflexes are normal and Babinski sign is negative. No sign of sensory or cerebellar deficit is appreciated.

Initial laboratory evaluation shows that the complete blood cell count, urine organic acid levels, creatinine kinase level, metabolic profile, chest radiograph, electrocardiogram, and echocardiogram were normal. He is also tested for fascioscapulohumeral muscular dystrophy, type 1 muscular dystrophy, short-chain acyl-coenzyme A dehydrogenase deficiency, medium-chain acyl-coenzyme A dehydrogenase deficiency, Prader-Willi syndrome, acycarnitine deficiency, and hypothyroidism, which are all negative. In addition, he also tests …