This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pediatrics
[{'content': 'An infant presents with hypotonia and hyporeflexia. During his intrauterine period, there was polyhydramnios and decreased fetal movements. Most probable diagnosis is – \nSelect and explain. \nA. Spinal muscular atrophy, B. Congenital myasthenia, C. Congenital myotonia, D. Muscular dystrophy', 'role': 'user'}, {'content': "Answer: A \nExplanation: Out of the given options only spinal muscular atrophy is able to cause hypotonia and hyporeflexia during infancy. Rest of them either present late in childhood or do not give the symptoms.\nPolyhydramnios and decreased fetal movements can occur in any neuromuscular disorder which present during intrauterine life.\nLets see each option one by one.\n\n\nSpinal muscular atrophy (SMA)\n\nSMA is a degenerative disease of motor neurons that begin in fetal life and continue to progress in infancy and childhood.\nThe cardinal features are:\nHypotonia\nGeneralized weakness\nAbsent tendon stretch reflexes\nInvolvement of tongue face and jaw muscle but sparing of extraocular muscle and sphincters.\n\nCongenital myotonia\n\nCongenital myotonia or myotonia congenita is a chloride channel defect of skeletal muscle.\nThere are weakness and generalized hypertrophy of muscles.\nIts ruled out as\n\n\nPresents in early childhood (2-3 years age)\nDeep tendon reflexes are preserved.\n\nCongenital myasthenia\n\nIt's a disease of neuromuscular junction similar to myasthenia gravis except that its not autoimmune but rather due to genetic mutations.\nIt presents in infancy and childhood with symptom similar to myasthenia gravis.\nIt can be ruled out as-\n\n\nIt does not present in the intrauterine life (so does not cause polyhydramnios).\nDTRs are preserved\n\nMuscular dystrophies\n\nMuscular dystrophy refers to a group of hereditary progressive diseases.\nIt includes\nDuchene's muscular dystrophy\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\nLimb-girdle\xa0\xa0\xa0\xa0\xa0\xa0\nCongenital myopathies\nBecker\xa0\xa0\nMyotonic dystrophic\nAll of these except congenital myopathies are easily ruled out as they present in childhood age. some may rarely present in infancy but never in the intrauterine life.\nCongenital myopathies are the most difficult one to rule out.\n\n\nThey present with hypotonia in infancy.\nIt may also present in intrauterine life.\nThe only reason I'm with 'Spinal muscular atrophy' is that congenital myopathy is a very rare disease.", 'role': 'assistant'}]