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Multisystem Disorders
Overview
For multisystem disorders, the diagnosis often depends on identifying the combination of neurologic and nonneurologic manifestations. For example, neuropathy plus macrocytic anemia should raise concern for B12 or folate deficiency. Confusion, neuropathy, and gastrointestinal (GI) distress might raise concern for lead poisoning. Seizures with fasciculations and profuse salivation suggest cholinesterase toxicity (nerve agent).
This section discusses some important multisystem disorders. This is not a complete list, but it is illustrative of the types of presentations and the diagnoses they suggest.
Nutritional Deficiencies
B12 Deficiency
Vitamin B12 deficiency is underdiagnosed. It can develop in the elderly, in vegetarians (especially vegans), and in people who have difficulty with absorption. The patient can present with cognitive, motor, and or sensory abnormalities. The term pernicious anemia is used when this occurs due to autoimmune causes. Macrocytic anemia is characteristic of B12 deficiency, and it looks very similar to what is seen with folate deficiency.
Neurologic complications can be in multiple locations, specifically the peripheral nerve, spinal cord, and brain. Common presentations of B12 deficiency are discussed here.
Cognitive Dysfunction memory disturbance and mood disturbance are the most common cognitive abnormalities. Psychosis can be seen (megaloblastic madness).
Neuropathy both motor and sensory disturbances are evident. The sensory changes are length dependent, so distal lower extremities are affected prior to proximal and upper extremities. The changes are sensory loss and paresthesias. Affected sensation is cutaneous and proprioceptive.
Myelopathy spinal cord involvement affects predominantly the dorsal columns and lateral tracts, resulting in loss of dorsal column sensation and corticospinal tract dysfunction with weakness and spasticity. Hence, there is a combination of upper and lower motor neuron dysfunction with B12 deficiency.
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