A 45-year-old, previously healthy man comes to the office due to worsening extremity weakness and numbness. Three months ago, the patient began experiencing numbness and weakness in both feet that made it difficult to climb stairs or stand up from a seated position. Two weeks later, he noticed weakness of his grip strength bilaterally but had no difficulty lifting his arms. The muscle weakness has been slowly progressing, and the patient now has difficulty buttoning his clothes, turning doorknobs, and walking on a level surface. He does not use tobacco or illicit drugs and drinks alcohol occasionally. Vital signs are within normal limits. Physical examination shows weakness of the small muscles of the hands and the hip girdle muscles bilaterally. Deep tendon reflexes are diffusely diminished, and there is loss of vibration and position sensation in the toes bilaterally. Which of the following findings is most likely to be associated with this patient's current symptoms?
Chronic inflammatory demyelinating polyneuropathy | |
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CSF = cerebrospinal fluid; LMN = lower motor neuron; NCS = nerve conduction studies. | |
This patient has progressive muscle weakness affecting both proximal (eg, standing up) and distal (eg, buttoning shirts) muscles, accompanied by lower motor neuron signs (eg, hyporeflexia, muscle atrophy) and sensation deficits. These findings are consistent with chronic inflammatory demyelinating polyneuropathy (CIDP), an acquired, immune-mediated disorder characterized by the demyelination of peripheral nerves and nerve roots.
In contrast to many other polyneuropathies (eg, diabetic), CIDP is not length dependent. Therefore, it classically causes both proximal (eg, hip girdle) and distal (eg, hand) muscle weakness. Symptoms develop over >8 weeks, distinguishing it from acute inflammatory demyelinating polyneuropathy. Motor symptoms predominate, but distal sensory loss (eg, in the toes) can also occur; vibration and position sense are often preferentially affected due to greater involvement of large, thickly myelinated fibers. In addition, because CIDP involves peripheral nerves, lower motor neuron signs (eg, hyporeflexia, atrophy) may be seen.
Diagnosis requires evidence of demyelination, either through nerve conduction studies showing decreased peripheral nerve conduction velocity or peripheral nerve biopsy showing histologic evidence of segmental demyelination. Treatment focuses on decreasing inflammation (eg, glucocorticoids, intravenous immunoglobulin).
(Choice A) Lambert-Eaton myasthenic syndrome results from autoantibodies against voltage-gated calcium channels and often causes proximal muscle weakness with hyporeflexia. However, it usually does not affect distal muscles or cause sensation defects.
(Choice C) Multiple sclerosis can cause a variety of neurologic deficits due to demyelinating plaques in the brain and spinal cord. However, because the plaques are located in the CNS, findings are rarely symmetric, and lower motor neuron signs (eg, hyporeflexia, atrophy) are typically absent.
(Choice D) An increased serum methylmalonic acid level is diagnostic for vitamin B12 deficiency, which can cause subacute combined degeneration (SCD). Although dorsal column damage in SCD results in diminished vibration and position sensation, spastic paresis with hyperreflexia (due to damage to the lateral corticospinal tracts) and ataxia (due to damage of the spinocerebellar tract) are also typically present.
(Choice E) Inflammatory myopathies (eg, polymyositis) result from inflammatory infiltrates causing necrosis of myofibers. In contrast to CIDP, proximal muscles in inflammatory myopathies are classically much more affected than distal muscles. In addition, because myopathies target musculature rather than nerves, sensation deficits and lower motor neuron signs (eg, hyporeflexia, atrophy) are unexpected.
Educational objective:
Chronic inflammatory demyelinating polyneuropathy causes immune-mediated destruction of myelin in a non–length dependent manner; this results in progressive weakness of both proximal and distal muscles, sometimes with distal sensory loss.