Infant: Hypotonia and weak cry

Case History

T was a 3.5 m.o. male. T is a bottle-fed infant with feeding difficulties. At the 2 months well visit, mom reported that feeding was slow, and T frequently coughed and gagged during feedings. The child also had a quiet cry, that was difficult to hear unless the parent was in the proximity of the child.

T’s mother routinely attempted tummy time. However, at the 2 month well visit, she noted that it was difficult for T to keep his head up and T rarely moved from the position in which she placed him. She also mentioned that T didn’t squirm as much as he used to.

During physical exam, the PCP noted that T was alert and responsive. However, when lying supine, T’s legs remained abducted in a “frog-legged position”. Decreased spontaneous and antigravity movement of the limbs were observed. Mild hypotonia was present; T exhibited head lag through the entirety of the pull to sit maneuver as well as a “U posture” upon completion of horizontal suspension. Additionally, T’s chest appeared bell shaped; only the diaphragm moved (abdominal breathing) during respiration.

Clinical Pearl: Although common amongst all infants, dysphagia may be an early indication of neuromuscular disease. When combined with hypotonia, weak cry, decreased limb movement, and the bell-shaped appearance of the chest due to intercostal weakness, the PCP should promptly refer to a specialist (consider pediatric neurology) for evaluation of SMA and genetic testing.

Given the combined hypotonia and paradoxical breathing, the PCP was concerned regarding T’s gross motor development. He was referred to a local neurologist who ordered an MRI that was read as abnormal (‘focal areas of pachygyria could be potentially present’). A spinal MRI was also done and was negative. The neurologist sent CK, serum amino acids, and TSH/FT4, all of which were normal. Urine organic acids were pending.


The PCP subsequently sent T to a pediatric neurologist at the nearest major medical center for a second opinion. At evaluation at 3.5 months. Socially, the child was very alert and responsive. Head lag persisted when pulled up from supine position. He did not bear weight on legs and did not have much extremity movement. Despite continued dysphagia, his growth was very good [MS1] and appropriate for age. Diaphragm breathing and intercostal weakness persisted. Genetic testing confirmed the diagnosis of SMA.

Clinical Pearl: The early diagnosis and the early treatment of spinal muscular atrophy (SMA) is essential to maximizing a child’s health outcomes. Delays in diagnosis are costly to the child’s long-term health as motor neuron loss occurs early in the progression of the disease, especially in children with SMA type I. Prognosis is improved with early treatment. If you suspect SMA do not delay; refer immediately to a specialist for genetic testing.