A 14-year-old boy is brought to the office due to lower back and buttock pain for 3 months. The pain is diffuse across the lower back and buttocks, worsens with activity, and resolves with rest. It occasionally radiates down the legs. There is no history of trauma. Vital signs are normal. Examination shows a subcutaneous lipoma over the lower back, mild scoliosis, and weak ankle dorsiflexion. Deep tendon reflexes are 1+ in the lower extremities and 2+ in the upper extremities. The lower extremities are thin and weak. What is the most likely diagnosis in this patient?

Question

A 14-year-old boy is brought to the office due to lower back and buttock pain for 3 months.  The pain is diffuse across the lower back and buttocks, worsens with activity, and resolves with rest.  It occasionally radiates down the legs.  There is no history of trauma.  Vital signs are normal.  Examination shows a subcutaneous lipoma over the lower back, mild scoliosis, and weak ankle dorsiflexion.  Deep tendon reflexes are 1+ in the lower extremities and 2+ in the upper extremities.  The lower extremities are thin and weak.  What is the most likely diagnosis in this patient?

Quizplus · Accepted Answer

11ec25c8_d57b_582c_bc81_9779eb6bf73c_MD0003_00 Although back pain in adolescents is usually benign and musculoskeletal in origin, the presence of neurologic deficits (eg, leg weakness, hyporeflexia) indicates a serious underlying condition. In this case, the most likely diagnosis is tethered cord syndrome, which is characterized by stretch-induced dysfunction of the spinal cord. This condition is closely associated with closed spinal dysraphism, which should be suspected in this patient with a gross lumbosacral abnormality (eg, lipoma). tethered cord syndrome lumbosacral abnormality In closed spinal dysraphism, the posterior arches fail to fuse while the overlying skin remains intact. As a result, the spinal cord may abnormally attach to surrounding tissues, such as a lipoma extending from the spinal canal to the subcutaneous tissue. As the child grows, the inferior end of the spinal cord remains fixed and stretches rather than rising in the spinal canal. Stretching of the cord due to repetitive movement exacerbates cord dysfunction and leads to progressive back, buttock, and leg pain, as well as sensory and motor dysfunction and diminished reflexes (ie, lower motor neuron signs). Pain is worse with exercise, and leg weakness due to muscle denervation can lead to gait abnormalities, muscle atrophy, and footdrop, as seen in this patient. Scoliosis can result from improper positioning to relieve back discomfort, and bladder/bowel dysfunction is also common. MRI of the spine is diagnostic. (Choice A) Ankylosing spondylitis is an inflammatory condition that commonly presents in adolescent boys with chronic lower back pain and stiffness; symptoms are worse, not better, with rest. Because pathophysiology involves the joints, muscle atrophy and hyporeflexia are not seen. (Choice B) Becker muscular dystrophy is an X-linked recessive disorder that presents in late childhood or early adolescence with proximal muscle weakness. Muscle atrophy with hyporeflexia can occur. However, chronic lower back pain would not be expected, and this patient's lumbosacral lipoma makes a tethered cord more likely. (Choice C) Guillain-Barré syndrome (GBS) is an immune-mediated polyneuropathy that can present with back pain and hyporeflexia. Unlike this patient's condition, GBS causes acutely progressive ascending paralysis. (Choice D) Disc herniation in adolescents is typically due to trauma and leads to lower back pain that is worse with flexion and radiates to the legs. This patient's lumbosacral lipoma and lack of trauma make this diagnosis less likely. Educational objective: Chronic back pain associated with neurologic deficits (eg, hyporeflexia, weakness) and a gross lumbosacral abnormality (eg, lipoma) should raise concern for tethered spinal cord with underlying spinal dysraphism. References: Spinal column shortening for tethered cord syndrome associated with myelomeningocele, lumbosacral lipoma, and lipomyelomeningocele in children and young adults. (http://www.ncbi.nlm.nih.gov/pubmed/28362188)

A 14-Year-Old Boy Is Brought to the Office Due to Lower