WBR0299

Author	[[PageAuthor::Ogheneochuko Ajari, MB.BS, MS [1] (Reviewed by Yazan Daaboul, M.D. and Alison Leibowitz [2])]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Embryology
Sub Category	SubCategory::Neurology
Prompt	[[Prompt::A 30-year-old woman presents to the emergency department for a burn lesion in her left hand. Upon further questioning, the patient reports that she has burned her fingers on many occasions recently because she is unable to feel the burning sensation. On physical examination, the patient has bilateral loss of pain and temperature in her upper extremities with preserved sensations of touch and vibration. Neurological examination of her lower extremities does not reveal any abnormalities. What is the most likely cause of this patient's symptoms?]]
Answer A	AnswerA::A deficiency of dietary supplements
Answer A Explanation	[[AnswerAExp::Vitamin B12 or vitamin E deficiency is associated with subacute combined degeneration, which affects the dorsal columns, lateral corticospinal tracts, and the spinocerebellar tracts. Typically, symptoms include ataxic gait and impaired sensations of touch, vibration, pressure, and propioception.]]
Answer B	AnswerB::Small fiber nerve damage caused by chronic uncontrolled diabetes mellitus
Answer B Explanation	[[AnswerBExp::Diabetic neuropathy is a peripheral neuropathy usually starts with small fiber neuropathy that is associated with paresthesias and loss of pain and temperature sensations. However, symptoms typically start in the lower extremities and progress upwards to involve the small fiber and large fiber autonomic, sensory, and motor neurons. Diabetic neuropathy is not classically associated with bilateral loss of pain and temperature sensations in the upper extremities.]]
Answer C	AnswerC::A tumor that arises from the membranous layers surrounding the central nervous system
Answer C Explanation	[[AnswerCExp::Meningioma is a tumor of the meninges, the membranous layers surrounding the central nervous system. Meningioma is associated with a progressive spastic weakness in legs, increased intracranial pressure, and focal seizures.]]
Answer D	AnswerD::Atrophy of the spinal muscles
Answer D Explanation	[[AnswerDExp::Spinal muscular atrophy is associated with muscle weakness, poor muscle tone, limpness, or a tendency to flop (the "floppy baby" syndrome).]]
Answer E	AnswerE::An abnormal fluid-filled spinal cord cavity
Answer E Explanation	[[AnswerEExp::Syringomyelia is an abnormal fluid-filled spinal cord cavity.]]
Right Answer	RightAnswer::E
Explanation	[[Explanation::Syringomyelia is a chronic neurological disease characterized by the presence of a syrinx, an abnormal fluid-filled spinal cord cavity. The lesion is usually located in the lower cervical region, where symptoms are frequently reported at a dermatome level that has a "cape-like" distribution. Since the spinothalamic tract cells cross just ventral to the central canal, the syrinx mainly affects the spinothalamic tract pathway (loss of pain and temperature), where an interruption occurs at the level of the axons that cross through the ventral spinal commissure. Patients may also present with complaints of recurrent bruises or burns in their upper extremities, given their inability to sense the pain and the burning sensation. In contrast, the dorsal column-medial lemniscus and corticospinal pathways are not affected in syringomyelia, and thus the the touch, vibration, proprioception, and pressure sensations (dorsal column-medial lemniscus) and voluntary movement (corticospinal pathway) remain intact. Syringomyelia is most commonly associated with Chiari I malformation (CMI), a congenital hindbrain malformation characterized by the caudal herniation of the cerebellar tonsils at least 3-5 mm below the foramen magnum. Patients with Chiari I malformation are usually asymptomatic at childhood and may present with syringomyelia during early adulthood (25-35 years of age) with neck pains, headaches, and cerebellar symptoms. Other causes of syringomyelia include trauma, brain tumors, and meningitis, but idiopathic syringomyelia is not uncommon. Educational Objective: Syringomyelia is an an abnormal fluid-filled spinal cord cavity. It can manifest in the bilateral loss of pain and temperature sensations due to involvement of the spinothalamic tract. Patients often present with multiple burns in their upper extremities due to loss of burning sensation. References: Naidich TP, McLone DG, Fulling KH. The Chiari II malformation: part IV. The hindbrain deformity. Neuroradiology. 1983;25:179-97 Milhorat TH, Chou MW, Trinidad EM, et al. Chiari I Malformation Redefined: Clinical and Radiographic Findings for 364 Symptomatic Patients. Neurosurgery. 1999;44(5):1005-17 First Aid 2014 page 446]]
Approved	Approved::Yes
Keyword	WBRKeyword::Loss of temperature sensation, WBRKeyword::Loss of pain sensation, WBRKeyword::Loss of pain and temperature, WBRKeyword::Syringomyelia, WBRKeyword::Chiari I malformation, WBRKeyword::Spinal cord
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