Although more closely associated with carpal tunnel syndrome, hypothyroidism is a recognized cause of peripheral neuropathy. While the mechanism of neuropathy in untreated hypothyroidism is unclear, researchers have theorized that it may be attributed to the deposition of mucopolysaccharides or to the accumulation of soft tissue edema in proximity to peripheral nerves. Regardless of the precise mechanism, it is hypothesized that these underlying metabolic derangements cause nerve entrapments resulting in the demyelinating polyneuropathy described in the literature. Symptoms including tingling, numbness and paresthesia are most often reported in the hands and feet of afflicted patients.
Clinical Case I
A 62 y/o male with untreated hypothyroidism* of a 8-10 year duration presented complaining of progressively worsening paresthesia and numbness in the forefoot bilaterally of a one year duration. Patient history was negative for degenerative disc disease, diabetes or alcoholism.
Labs: Comprehensive Metabolic Panel, Vitamin B12, Folate, ESR, Lyme disease antibody and Free T4 were negative. TSH was elevated.
Neurological Testing: Office-based screening revealed reduced sharp sensation in the left foot, normal 10gm monofilament testing and reduced vibratory sensation as documented by a timed vibration test with the ETF (TVT 7.4s right hallux, 8.4s left hallux).
*The patient notes being placed on thyroid hormone replacement therapy after his initial diagnosis. He admits to going against medical advice and discontinuing it after several months.
Clinical Case II
A 54 y/o male with undiagnosed hypothyroidism presented with progressive numbness in the toes over past 1-2 years. Patient history was negative for degenerative disc disease, diabetes or alcoholism.
Labs: Random blood glucose, Vitamin B12, Folate, Lyme disease antibody were negative. TSH was elevated and Free T4 was below normal.
Neurological testing: Office-based screening revealed reduced sharp sensation at the hallux bilaterally, normal 10gm monofilament test and reduced vibratory sensation as documented by a timed vibration test with the ETF (TVT 7.5s right 5th metatarsal head, 7.6s left 5th metatarsal head).
NCV/EMG testing confirmed peripheral neuropathy consistent with a demyelinating process in the feet bilaterally.
Although an uncommon cause of peripheral neuropathy, undiagnosed or untreated hypothyroidism should be suspected in cases where more obvious etiologies are ruled out. Fortunately, patient symptoms often resolve with appropriate thyroid hormone replacement therapy over a 6-12 month period if treated promptly.