Hindsight Is 20/20

A glycosylated hemoglobin (HbA1c) level was 6.2%. Methylmalonic acid was 69 nmol per liter (normal range, 45-325). Antibodies to Borrelia burgdorferi and Treponema pallidum were absent. Impaired glucose metabolism was the leading diagnosis for her polyneuropathy, and it was recommended that she undergo an oral glucose tolerance test. Electromyography was not performed.

The neurological symptoms are now chronic, and importantly, the patient has developed sensory deficits on neurological examination, suggesting worsening of the underlying process. While the paresthesia is now limited to a “stocking/glove” distribution consistent with distal sensory polyneuropathy, there should still be a concern for spinal cord pathology given that the HbA1c level of 6.2 would not explain her initial distribution of symptoms. Myelopathy may mimic peripheral nerve disease if, for example, there is involvement of the dorsal columns leading to sensory deficits of vibration and proprioception. Additionally, the transient episode of upper extremity numbness raises the question of sensory nerve root involvement (ie, sensory radiculopathy). Unexplained abdominal pain could possibly represent the involvement of other nerve roots innervating the abdominal wall. The patient’s episode of focal arm numbness recalls the lancinating radicular pain of tabes dorsalis; however, the negative specific treponemal antibody test excludes neurosyphilis.

The differential diagnosis going forward will be strongly conditioned by the localization of the neurological lesion(s). To differentiate between myelopathy, radiculopathy, and peripheral neuropathy, I would perform nerve conduction studies, magnetic resonance imaging (MRI) of the spinal cord, and cerebrospinal fluid analysis.

The patient began taking a multivitamin, and after weeks her paresthesia had resolved. One month later, she developed an intermittent, throbbing left-sided headache and pain behind the left eye that was worsened with ocular movement. She then noted decreased visual acuity in her left eye that progressed the following month. She denied photophobia, flashers, or floaters.

In the emergency department, visual acuity was 20/25 in her right eye; in the left eye she was only able to count fingers. Extraocular movements of both eyes were normal as was her right pupillary reflex. Red desaturation and a relative afferent papillary defect were present in the left eye. Fundoscopic exam demonstrated left optic disc swelling. The remainder of her cranial nerves were normal. She had pronation of the left upper extremity and mild right finger-to-nose dysmetria. Muscle tone, strength, sensation, and deep tendon reflexes were normal.

The improvement in the sensory symptoms was unlikely to be related to the nutritional intervention and provides a clue to an underlying waxing and waning illness. That interpretation is supported by the subsequent development of new visual symptoms and signs, which point to optic nerve pathology. Optic neuropathy has a broad differential diagnosis that includes ischemic, metabolic, toxic, and compressive causes. Eye pain, swelling of the optic disc, and prominent impairment of color vision all point to the more specific syndrome of optic neuritis caused by infections (including both Treponema pallidum and Borrelia species), systemic autoimmune diseases (systemic lupus erythematosus or Sjogren’s syndrome), and central nervous system (CNS) demyelinating diseases. Of these, inflammatory demyelinating processes would be the likeliest explanation of intermittent and improving neurologic findings.