Working Diagnosis:
Hypothyroidism-induced peroneal neuropathy

Treatment:
Patient was restarted on levothyroxine 50mcg/day with a plan to titrate up every 4 weeks

Outcome:
As an outpatient, the patient had EMG which showed evidence of severe right peroneal neuropathy. Her symptoms improved once restarted on thyroid hormone replacement therapy. She was able to resume her usual activities and is seeing PT on an outpatient basis for foot drop.

Author's Comments:
This case illustrates the potential for cognitive bias and the importance of obtaining a full history. Despite a known history of hypothyroidism and no recent TSH value on record, this patient was seen three separate times without having a TSH checked. The physical exam was not consistent with lumbar radiculopathy and was more consistent with peripheral neuropathy. In situations where there are inconsistencies between the physical exam and imaging findings, a thorough medical history, though often overlooked, is important. However, because of cognitive biases including recency and anchoring bias, three MRIs were ordered with the potential for two additional MRIs if they had not been canceled. Recognizing that peripheral neuropathies are relatively common in hypothyroidism and especially being aware of our own cognitive biases will help to provide a higher level of care in all patient populations.

Editor's Comments:
This case underscores several key elements when evaluating patients with recurrent pain. Patients will often come into the office or present to the emergency department complaining of severe pain. When seen in the emergency department this will oftentimes lead to expensive tests required to rule out surgical emergencies that may not truly be warranted. In this case, this patient presented three times to the emergency department with each visit leading to additional expensive testing and eventually an admission before a diagnosis could be established. It is easy for providers to disregard pain when there is no discernable reason for it based on advanced imaging. This is exactly the time that a thorough history and physical exam should be performed in order to direct patient care. This patient’s presentation mostly involved weakness in the distal lower extremity with some associated numbness below the knee making a peripheral neuropathy a more likely diagnosis than a central nervous system lesion. The emergency department focused primarily on central nervous system lesions as those are more likely to require urgent or emergent intervention. In a primary care setting this patient may have had more time to speak with her providers about her symptoms and possibly avoid multiple expensive visits to the emergency department and a hospital admission. Peripheral neuropathies are common in the general population with a prevalence of 1% to 7%. These remain idiopathic in 25% to 46% of cases but the most common causes are diabetes mellitus, nerve compression or injury, alcohol use, toxin exposure, hereditary diseases and nutritional deficiencies. As such, any patient with a presentation of peripheral neuropathy should undergo basic screening lab work including a TSH, CBC, CMP, fasting blood glucose and vitamin B12. If the TSH had been performed at her initial presentation to the emergency department, then the further testing could have been avoided.

References:
Dyck PJ, Lambert EH. Polyneuropathy associated with hypothyroidism. J Neuropathol Exp Neurol. 1970 Oct;29(4):631-58. doi: 10.1097/00005072-197010000-00008.

Fabbri VP, Valluzzi A, Acciarri N, Foschini MP. Peripheral nerve mucoid degeneration involving the sciatic nerve. Pathologica. 2019;111(2):67-69. doi:10.32074/1591-951X-9-19

Castelli G, Desai KM, Cantone RE. Peripheral Neuropathy: Evaluation and Differential Diagnosis. Am Fam Physician. 2020 Dec 15;102(12):732-739. PMID: 33320513.

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