MON-422 Pyramidal Tract Dysfunction: A Rare Complication of Hyperthyroidism

Abstract Disclosure: M. Park: None. H. Angammana: None. E. Ogbu: None. M. Ali: None. A. Sajan: None. Introduction: Pyramidal tract dysfunction, though rare, has been reported in hyperthyroidism. This presentation poses a diagnostic challenge, as it can overlap with other neurological conditions, such as spinal cord dysfunction or brain lesions. We report a case of hyperthyroidism with pyramidal signs. Case report: A 34-year-old Hispanic woman with no past medical history presented with 4 weeks of progressive bilateral lower extremity weakness. She initially experienced generalized weakness that progressed to an unsteady gait. The patient also reported new-onset urinary urgency, incontinence, fatigue and diarrhea. She was normotensive (122/60 mmHg), with a heart rate of 82 beats/min and a temperature of 97.7 °F. On examination, she exhibited hyperreflexia in both upper and lower extremities, along with positive Hoffman’s and Babinski’s signs. Sensory examination was intact. Initial lab results showed normal potassium level of 3.8 mEq/L [3.5-5.3], and a low thyroid-stimulating hormone (TSH) of <0.01 IU/mL [0.45-5.33]. A computed tomography scan of the brain excluded spinal compression. Neurology evaluated the patient and suspected demyelinating disorders. Autoimmune workups were recommended, along with magnetic resonance imaging of the thoracic and lumbar spine, both of which returned negative. A lumbar puncture attempt was unsuccessful. Meanwhile, elevated thyroid-stimulating immunoglobulin (TSI) of 25.70 IU/L [0.00-0.55], thyrotropin receptor antibody (TRAb) of 24.40 IU/L [0.00-1.75], and an elevated free thyroxine (FT4) level of >7.77 ng/dL [0.82-1.77], along with a hypervascular gland on thyroid ultrasound, confirmed the diagnosis of Graves’ disease and patient was started on methimazole. These symptoms significantly improved following the initiation of methimazole. A follow-up at 1 month showed normalized thyroid function tests and complete resolution of weakness. Discussion: Pyramidal tract dysfunction associated with hyperthyroidism is a rare neuromuscular disorder. Patients present with muscle weakness and upper motor neuron (UMN) signs such as hyperreflexia, clonus, and extensor plantar responses. Some may also exhibit bladder spasticity and lower motor neuron signs in conjunction with the UMN features. The pathophysiology remains unclear, but the condition is known to be reversible with treatment to normalize thyroid function. The rarity of UMN signs in hyperthyroidism complicates the diagnosis, as these symptoms are more commonly seen in motor neuron disease prompting investigations into other neurological conditions as was done in our patient. Conclusion: This case highlights the rarity of UMN signs in hyperthyroidism which is one of the reversible causes of pyramidal tract dysfunction. Presentation: Monday, July 14, 2025