Neonatal Poliomyelitis
Neonatal poliomyelitis is extremely rare in the United States. It is caused by polio virus infection. Neonates may be infected by exposure to a recently vaccinated sibling. Polio virus has affinity for the alpha motor neurons of the anterior horn of the spinal cord and cranial nerve motor nucleus.
Weakness and hypotonia are diffuse but usually asymmetrical. Dynamic tone is decreased. Pleocytosis and increased protein are usually present in the cerebrospinal fluid. The diagnosis is established by viral isolation from the stool.

Hypotonia due to nerve involvement has few distinguishing characteristics (Figure 134.1). Dynamic tone is usually decreased. Hypotonia and weakness occur to a similar degree (Figure 134.1). Large thick nerves (auricular nerve hypertrophy) may be present. Signs of peripheral nervous system sympathetic autonomic dysfunction may be present. Laboratory investigations are often needed to diagnose hypotonia due to nerve problems. Nerve conduction velocity, especially sensory nerve conduction velocity, may be decreased. H-reflexmay demonstrate slow proximal nerve conduction prior to the presence of distal slow nerve conduction velocity in routine nerve conduction studies. Slow sensory nerve conduction velocity is the major electrophysiologic clue to the diagnosis of peripheral nerve disease but it is not always present. Electromyography shows fibrillations. Motor unit potentials tend to be normal or slightly prolonged and large. Cerebrospinal fluid protein may be elevated. Autonomic responses to electrical and chemical stimulation may be abnormal. Nerve biopsy shows myelin or axonal abnormalities or both.

Figure 134.1.— Salient features of generalized hypotonia due to nerve disease. Arrow indicates the anatomical location of the injury; S & M: sensory and motor; SNAPS: sensory nerve action potentials; EMG: electromyogram; CSF: cerebrospinal fluid; PR: protein; WBC: white blood cells; IC: intracutaneous.

Diseases that involve the peripheral nerve in the neonatal period are: (1) neuronal-axonal disease not associated with Werdnig-Hoffmann disease, (2) giant axonal neuropathy, (3) infantile porphyria, (4) congenital sensory neuropathy with anihidrosis, (5) congenital hypomyelinative neuropathy, (6) Riley-Day syndrome, (7) acute polyneuropathy, (8) chronic inflammatory demyelinating polyneuropathy, and (9) congenital sensory neuropathy. Neuropathy can be classified as axonal, hypomyelinative, or demyelinating, and as sensory, motor, sensory-motor, or sensory-autonomic.
Five axonal neuropathies occur in the newborn period: giant axonal neuropathy, axonal polyneuropathy not associated with Werdnig-Hoffmann disease, the neuropathy that accompanies infantile porphyria, congenital sensory neuropathy with anhidrosis, and Riley-Day syndrome. All the neonatal neuropathies that affect myelin involve the thick myelinated fibers and produce slow sensory nerve conduction velocities. Sensory neuropathies apparently produce hypotonia by damaging the sensory fibers that feed information to the alpha motor neurons.