MKSAP Quiz: a 1-week history of paresthesias
Updated guidelines issued for fall prevention in the elderly
A 53-year-old woman is evaluated in the office for a 1-week history of paresthesias that began symmetrically in the feet and progressed to involve the distal legs and, more recently, the hands. She says she is unsteady when walking, has lower limb weakness, and has difficulty going upstairs. The patient has no history of pain or bowel or bladder impairment. Personal and family medical history is noncontributory, and she takes no medications.
On physical examination, vital signs are normal. Weakness of distal lower extremity muscles is noted, with stocking-glove sensory loss and areflexia. Deep tendon reflexes are absent. Plantar responses are flexor, and gait is unsteady. No sensory level is present across the thorax. Mental status, language, and cranial nerve function are normal.
Complete blood count results, erythrocyte sedimentation rate, serum creatinine and creatine kinase levels, and liver chemistry test results are normal.
A chest radiograph shows no abnormalities.
Which of the following is the most appropriate next diagnostic test?
A. Electromyography
B. MRI of the spinal cord
C. Serologic testing for West Nile virus
D. Sural nerve biopsy
MKSAP Answer and Critique
The correct answer is A) Electromyography. This item is available to MKSAP 15 subscribers as item 19 in the Neurology section.
This patient should undergo electromyography (EMG). She has a rapidly progressive disorder affecting the peripheral nervous system, most compatible with a clinical diagnosis of Guillain-Barré syndrome. Patients with Guillain-Barré syndrome typically develop paresthesias distally in the lower extremities that are followed by limb weakness and gait unsteadiness. In addition to sensory loss and limb weakness, deep tendon reflexes are characteristically absent or markedly reduced. The diagnosis is confirmed by EMG, which usually shows a demyelinating polyradiculoneuropathy. Cerebrospinal fluid (CSF) analysis characteristically shows albuminocytologic dissociation, whereby the spinal fluid cell count is normal but the spinal fluid protein level is elevated. CSF analysis may also yield normal results early in the course of the disease. However, a normal CSF cell count is useful in excluding other infectious conditions, such as polyradiculoneuropathies associated with HIV and cytomegalovirus infection, infection due to West Nile virus, and carcinomatous or lymphomatous nerve root infiltration. By definition, symptoms in patients with Guillain-Barré syndrome peak within 4 weeks of onset. Poor prognostic features include rapid symptom progression, respiratory failure, EMG evidence of axonal degeneration, and advanced age. Intravenous immune globulin and plasma exchange are equally efficacious in the treatment of Guillain-Barré syndrome.
MRI of the spinal cord would be inappropriate as the next diagnostic test. The patient's presentation of distal extremity sensory loss with areflexia suggests a disorder of the peripheral nervous system. A spinal cord lesion (myelopathy) would be an unlikely cause of the symptoms noted on clinical examination. The absence of bowel or bladder impairment, the lack of a sensory level across the thorax, and the upper and lower limb areflexia argue against a central nervous system disorder affecting the spinal cord.
West Nile virus infection should be considered in every patient with symptoms of extremity weakness that begin acutely and progress over days to weeks. However, the presence of paresthesias and sensory loss on examination are not typical of West Nile virus infection. This enteroviral illness affects the anterior horn cells, causing limb weakness in the absence of sensory loss. Most cases of West Nile virus infection cause only minor symptoms that are indistinguishable from those of other viral illnesses.
Biopsy of the sural nerve is considered in the diagnostic evaluation of patients with a marked peripheral neuropathy of unknown cause. The sural nerve is a sensory nerve that supplies sensation to the lateral distal leg and lateral aspect of the foot. Sural nerve biopsy is appropriate in patients with suspected vasculitis or amyloidosis and occasionally in patients with chronic inflammatory demyelinating polyradiculoneuropathy; it is also used to exclude neuropathic conditions resulting from neoplastic infiltration or other inflammatory conditions, such as sarcoidosis. Symmetric signs and symptoms and diffuse areflexia are not typical of vasculitis. The acute onset and rapid symptom progression would argue against amyloidosis, chronic inflammatory demyelinating polyradiculoneuropathy, or other infiltrating peripheral nerve disorders. Sural nerve biopsy is not necessary in patients with suspected Guillain-Barré syndrome.
Key Point
- Guillain-Barré syndrome is a disorder associated with rapidly progressive extremity weakness, paresthesias, and areflexia.