Probably, most instances are immune, paraneoplastic, or postinfectious in nature. The same pattern of sensory loss evolving in a subacute or chronic manner is well known to occur as a paraneoplastic illness, described further on in this chapter, but it can evolve over days, or in association with the Sjögren syndrome, scleroderma, lupus erythematosus, paraproteinemia, HIV and human T-cell lymphotropic virus type I (HTLV-I) infection. Certain drugs and other agents, especially cisplatin and excessive intake of pyridoxine, are also causes of a sensory neuronopathy. These are discussed again later, under “Drug-Induced Neuropathies and Neuronopathies.” A rare form of “ataxic GBS” involves solely the large sensory fibers and produces ataxia, thereby simulating an acute sensory neuronopathy. In GBS, however, there is usually some degree of proximal weakness and the sensory changes do not extend to the face and trunk.
The neurotoxic effects of Corynebacterium diphtheriae and the mode of action of the exotoxin elaborated by the bacillus are described in Chap. 41. Local action of the exotoxin may paralyze pharyngeal and laryngeal muscles (dysphagia, nasal voice) within 1 or 2 weeks after the onset of the infection and shortly thereafter may cause blurring of vision because of paralysis of accommodation, but these and other cranial nerve symptoms may be overlooked. At this stage, the cranial neuropathy must be distinguished from that of GBS, botulism, and most of all, from myasthenia gravis.
A polyneuropathy, appearing 5 to 8 weeks later, takes the form of an acute or subacute limb weakness with paresthesias and distal loss of vibratory and position sense. The weakness characteristically involves all extremities at the same time or may descend from arms to legs. The patient may be unable to stand or walk and occasionally the paralysis is so extensive as to impair respiration. The CSF protein is usually elevated (50 to 200 mg/dL). Deaths that occur after the pharyngeal infection has subsided are a result of cardiomyopathy or, less often, of severe polyneuropathy with respiratory paralysis. This type of polyneuropathy, now quite rare, should be suspected in the midst of an outbreak of diphtheritic infection, as occurred in Russia (Logina and Donaghy).
The important pathologic change is one of segmental demyelination without inflammatory reaction of spinal roots, sensory ganglia, and adjacent spinal nerves. Anterior horn cells, axons, peripheral nerves distally, and muscle fibers remain normal (Fisher and Adams).
Treatment Diphtheria antitoxin, given within 48 h of the onset of the infection, reduces the incidence and severity of neuropathic complications. Antitoxin is probably of little value once the polyneuropathy begins. Thereafter, treatment is purely symptomatic, along the lines indicated for GBS. The prognosis for full recovery is excellent once respiratory paralysis is circumvented.