Hypotonia: A Clinical Sign, Several Possible Aetiologies

Background: Hypotonia is defined as a decrease in muscle resistance to passive movement. It is easily recognized in the observation of the newborn (NB), being a frequent sign of disease in this age group.

Clinical cases:

Case 1: Male NB, childbirth by cesarean section at 35 weeks, Apgar score 2/8/8 needing hospitalization in the NICU and ventilatory support. Because of generalized hypotonia, muscular weakness and weak primitive reflexes, a Neuropediatrics evaluation was made at D2 of life. It was observed: batrachian position, facial hypomimia, bilateral eyelid ptosis without ophthalmoparesis and reactive pupils; sialorrhea, compromised swallowing and cough reflexes; narrow chest with predominantly abdominal breathing; poor muscle masses, flaccid quadriparesis, absent reflexes and arthrogryposis. His mother showed a myopathic face and a clear myotonic phenomenon. Genetic studies confirmed the diagnosis of myotonic dystrophy type 1. The NB left the hospital in D113 of life under non-invasive ventilation, physiotherapy and nasogastric tube feeding.

Case 2: Male infant with healthy parents, normal gestational and neonatal periods. He was derived for a Neuropediatrics observation with 1 month of age due to hypotonia, hyporeflexia, and poor active movements and primitive reflexes. On neurological examination, he presented good fixation and eye movements, apparent fasciculations of the tongue, severe axial and peripheral hypotonia, without spontaneous movement observed, bell-shaped chest, inter-bone muscle amyotrophy, areflexia and paradoxical breathing. The genetic study supported the diagnosis of spinal muscular atrophy type 1. He started on intrathecal Nusinersen and physiotherapy.

Both cases maintain a multidisciplinary follow-up.

Conclusions: Hypotonia is a nonspecific sign with many possible underlying aetiologies (from central nervous system to the muscle itself). The clinical history and neurological examination are vital, providing clues to a methodical and systematic investigation. It is essential to accomplish an early etiological diagnosis to implement adequate therapy (when available), establish prognosis and offer genetic counselling.