Leyenaar.qxd 8/26/2005 4:03 PM Page 397 NEUROLOGY SUBSPECIALTY ARTICLE A schematic approach to hypotonia in infancy JoAnna Leyenaar MD MPH, Peter Camfield MD FRCPC, Carol Camfield MD FRCPC J Leyenaar, P Camfield, C Camfield. A schematic approach Une démarche schématique envers l’hypotonie to hypotonia in infancy. Paediatr Child Health 2005; pendant la première enfance 10(7):397-400. L’hypotonie peut être le signe révélateur de nombreuses maladies Hypotonia may be the presenting sign for many systemic diseases and systémiques ou du système nerveux. Le présent article traite d’une diseases of the nervous system. The present paper discusses a rational, démarche diagnostique rationnelle, simple et précise envers l’hypotonie simple and accurate diagnostic approach to hypotonia in infancy, pendant la première enfance, illustrée par le cas d’une fillette de cinq mois illustrated by the case of a five-month-old infant girl recently referred récemment aiguillée vers le IWK Health Centre de Halifax, en Nouvelle- to the IWK Health Centre in Halifax, Nova Scotia. Key points in the Écosse. Les principaux points de l’anamnèse et de l’examen physique sont history and physical examination are outlined to allow a tailored exposés afin de permettre une exploration personnalisée de la patiente et investigation both for the patient and for other hypotonic infants. A des autres nourrissons hypotoniques. Un exposé sur une importante discussion of an important neuromuscular disease, diagnosed in the maladie neuromusculaire, diagnostiquée chez la patiente, conclut l’article. present patient, concludes the paper. Key Words: Hypotonia; Infant; Spinal muscular atrophy nfants with hypotonia pose challenges for clinicians respiratory syncytial virus-positive bronchiolitis. The family Ibecause hypotonia may be the presenting sign of both history was unremarkable and there was no consanguinity. benign and serious conditions. On first glance, the magni- The infant’s mother had antiphospholipid syndrome. There tude of the differential diagnosis, the rarity of associated ill- was a seven-year-old, healthy male sibling. nesses, and the ongoing advances in diagnosis and On examination, the infant looked well, with no dys- management may appear overwhelming. morphic features. Height, weight and head circumference The present paper discusses a practical approach to were between the 75th and 90th percentiles. She had a hypotonia in infancy. Key elements in the child’s develop- strong cry and no fasciculations of the tongue were noted. mental and medical history and physical examination are Respiratory, cardiovascular and abdominal examinations outlined. The case of a five-month-old infant girl, recently were normal. Cranial nerves were normal, including seen at the IWK Health Centre in Halifax, Nova Scotia, extraocular movements. She had marked hypotonia on hor- provides a basis for discussion. izontal and vertical suspension. Tightness of the hip adduc- tors and knee extensors was noted. She had a weak grasp CASE PRESENTATION and was unable to reach forward. Primitive reflexes were A five-month-old infant girl was brought to her family absent. Deep tendon reflexes could not be elicited. physician after a family friend expressed concern that she was unable to raise her upper body when lying prone. Her Step 1: Understanding the terminology parents stated that she had made no attempts to roll over, A key distinction is to determine whether the infant has rarely moved her legs and made no attempts to push with low tone with or without muscle weakness. Tone is her feet when held upright. She put toys into her mouth defined as the resistance of muscles to stretch (1); there- using both hands but did not reach farther than 10 cm for fore, hypotonia is diminished resistance of muscles to pas- objects before her. She laughed and interacted with those sive stretching. With respect to infantile hypotonia, it around her and became excited at the sight of food. She may be considered the “least resistance that an alert (but breastfed well and seemed to have tolerated the recent not overstimulated) infant generates while opposing pas- introduction of rice cereal without coughing, choking or sive movement” (2). In contrast, weakness is diminished vomiting. She often squealed and seemed to respond to her muscle power or strength. While weak infants are always name. No loss of milestones was reported. hypotonic, hypotonia is often present with normal She had been born at 38 weeks by spontaneous vaginal strength (2). delivery with no prenatal or postnatal concerns. Apgar Hypotonia is caused by disorders that affect any level of scores were 8 at 1 min and 5 min, with points lost for colour the nervous system – brain, brain stem, spinal cord, periph- and tone. At three months, she had been hospitalized for eral nerves, neuromuscular junction and muscle. Figure 1 Department of Pediatrics, Dalhousie University, IWK Health Centre, Halifax, Nova Scotia Correspondence: Dr Peter Camfield, IWK Health Centre, 5850 University Avenue, PO Box 3070, Halifax, Nova Scotia B3J 3G9. Telephone 902-470-8479, fax 902-470-8486, e-mail [email protected] Paediatr Child Health Vol 10 No 7 September 2005 ©2005 Pulsus Group Inc. All rights reserved 397 Leyenaar.qxd 8/26/2005 4:03 PM Page 398 Leyenaar et al difficulties and failure to thrive. Therefore, a detailed feeding history from birth may provide valuable diagnostic clues. A Nerve • Congenital diagnosis of infantile botulism may be prompted by a history hypomyelinating neuropathy of honey or corn syrup consumption; contamination of these • Familial dysautonomia • Infantile neuraxonal products with Clostridium botulism may account for up to 20% Central Nervous degeneration of botulism cases during infancy (1). The family history may System • Chromosome be very revealing: a history of repeated abortions may suggest disorders (ie. Prader-Willi) . a variety of disorders with prenatal onset, developmental • Metabolic diseases . Muscle • Spinal cord injuries • Muscular delay (a chromosomal abnormality), delayed motor mile- dystrophies • Cerebral Motor stones (a congenital myopathy) and premature death (meta- dysgenesis • Metabolic Neuron myopathies • Hypoxic-ischemic bolic or muscle disease). injuries • Spinal • Central core muscular disease/fibre atrophies myopathies • Other Step 3: The physical examination Neuromuscular Junction congenital myopathies • Congenital and transient The physical examination typically narrows the differential myasthenia gravis • Infantile botulism diagnosis markedly. The degree of hypotonia may be initially inferred by assessing the infant’s posture while supine; truly Figure 1) Anatomical-clinical correlation illustrating differential diag- hypotonic infants may lie ‘frog-legged’, with hips adducted nosis of hypotonia in infancy and knees flexed. A lack of spontaneous movement suggests weakness. illustrates common diseases with hypotonia as a prominent In assessing tone, the child should be alert but not cry- feature and their anatomical correlates. ing. Extremity tone is readily assessed by passive movements. The term ‘benign congenital hypotonia’ was historically Truncal and nuchal tone may be best examined using tests of used as a diagnosis for infants who were hypotonic in the horizontal and vertical suspension. On vertical suspension, a absence of other signs and symptoms, and who had normal healthy infant should maintain the head upright and mid- tone in later childhood. We urge caution in the use of this line without slipping through the examiner’s hands. On ‘diagnosis of exclusion’, especially because it requires many horizontal suspension, the infant should maintain a straight months of follow-up for confirmation. One author argues back with the head upright and limbs flexed. In contrast, that benign congenital hypotonia has not been an appropri- hypotonic infants may wrap over the examiner’s arms. ate diagnosis since the 1960s, when central core disease and While strength may be measured in adults and older a number of other congenital myopathies were described (3). children using a standardized five-point scale, the ability to point, reach and lift may provide more helpful information Step 2: Key elements in the patient’s history in infants (1). Encouraging the caregiver to become Although the list of conditions to be considered in the dif- involved in this portion of the examination may provide ferential diagnosis of hypotonia in infancy is long, the valuable information. Abilities will need to be compared patient’s history may narrow the possibilities significantly. with age-appropriate developmental norms. Details of the pregnancy, delivery and postnatal period are The deep tendon reflexes are likely the most valuable important – a history of preterm delivery; toxoplasmosis, aspect of the physical examination. Brisk reflexes or clonus other infections, rubella, cytomegalovirus infection and indicate CNS dysfunction, while diminished or absent herpes simplex; neonatal seizures; drug and alcohol use; or reflexes point strongly to disorders of the lower motor unit. other pre- or postnatal insult increases the probability of Dysmorphic features sharply increase the likelihood of central nervous system (CNS) dysfunction as the underly- CNS dysfunction as an explanation for hypotonia, although ing etiology for low tone. A history of hip subluxation or a long, narrow face may indicate muscle weakness. Anterior arthrogryposis increases the likelihood of hypotonia in horn cell disease usually spares extraocular muscles,