Role of dermatomal somatosensory evoked potential in localizing the site of transverse myelitis.

Role of dermatomal somatosensory evoked potential in localizing the site of transverse myelitis Clinical Presentation A 12-year-old female, with mild upper respiratory tract infection one month ago, presented with bilateral lower limb weakness and urinary retention for one day. She felt sudden numbness in both thighs then weakness of both legs that progressed to inability to walk within 6-10 hours. There was no history of back pain, no trauma, no fever, no breathing or swallowing difficulty. Power was reduced to 1/5 in both ankles, and 3/5 in both knees and hip movements. Ankle jerk was absent bilaterally on presentation and mute planters. Knee jerk was normal on the right and exaggerated on the left. There were no sensory changes in the lower limbs. An MRI of the lumbosacral spine and CT brain were normal. Sensory-motor conductions including F wave study were normal. The H-reflexes and tibial somato-sensory evoked potentials were normal. She was given pulse steroid therapy and Acyclovir. She started moving her ankles with power 2/5, both ankle jerks were exaggerated with upgoing planters. Notice: Authors are encouraged to submit quizzes for possible publication in the Journal. These may be in any field of Clinical Neurosciences, and should approximately follow the format used here. Please address any submissions to the Assistant Editor, 1. How do you explain the persistence of H-reflex in the absence of ankle jerk? 2. What are the additional preferred electro-diagnostic tests, and why? 3. In view of the DSSEP, where do you localize the lesion (anatomically)? 4. What is the final diagnosis? Figure 1-The DSSEP study was carried out by placing densely packed recording electrodes 2 cm behind the central transverse array of international 10-20% system of EEG recording. Stimulation was carried out by placing electrodes in the cutaneous dermatomes, especially areas of subjective changes of sensation (called signature areas). Note that the best P1 and N1 potentials were recorded in the CZ'-FZ derivation. The P1 latency is 44 msec (normal). DSSEP-dermatomal short latency somatosensory evoked potentials. Figure 2-The DSSEPs simulating the S2 dermatome at the back of the thigh. Note that P1 and N1 potentials were absent. DSSEP-dermatomal short latency somatosensory evoked potentials.