12 Cases: where, when, what

Where. The examination that matters most here takes about a minute, and it is the reflexes. They are absent everywhere, and areflexia moves the lesion out of the brain and spinal cord and into the motor unit. The distal tingling then rules out the horn cell, the junction and the muscle, which are all purely motor, and leaves the nerves and roots. Guillain-Barré syndrome is a polyradiculoneuropathy, so if you chose nerve or root, you were right. The weakness on both sides of the face does not mean a second lesion. The facial nerves are peripheral nerves, and the same process can reach them.

When. The weakness has climbed over four days, beginning two weeks after an infection. A course measured in hours to days points to an immune or inflammatory cause.

What. Guillain-Barré is the diagnosis, but the list has to protect two others. Tick paralysis looks the same and is cured by finding the tick. A cord lesion can also look the same in its first days, because an acute, severe upper motor neuron lesion produces spinal shock, a flaccid, areflexic paralysis (DeMyer, pp. 273-274). Here the search for a sensory level found none and the bladder was normal, and those two findings kept the localization in the nerves and roots.

The traps. The first is calling a child who "won't walk" behavioral before anyone has picked up the reflex hammer, since absent reflexes cannot be produced on purpose. The second concerns the breathing count. It did nothing to help you localize, yet it is the examination you will repeat every few hours, because in Guillain-Barré the danger lies with the diaphragm and the autonomic nervous system rather than with the legs.

In where, when, what form: "Peripheral nerve and root, acute over days after an infection, most likely Guillain-Barré syndrome, with tick paralysis and an early cord lesion excluded at the bedside."

Where. In an infant who cannot tell you anything, the examination you choose decides the localization. Ptosis that worsens as you examine, a suck that fades after a few seconds and a cry that weakens are fatigable bulbar and ocular weakness. That pattern is the signature of the neuromuscular junction. The other great cause of a weak, alert, floppy infant is spinal muscular atrophy, and two findings argue against it here. Her tongue has no fasciculations, and her eyelids and eye movements are weak, whereas spinal muscular atrophy spares the eye muscles.

When. The course is measured in days, and a week ago this baby held her head well. The problem is therefore neither congenital nor static, which moves congenital myasthenic syndromes and cerebral palsy to the bottom of the list.

What. Infant botulism should be suspected in an infant under 6 months with constipation, listlessness, poor feeding, a weak cry and a reduced gag (Peredo 2009), and this baby has exactly that presentation. The constipation belongs to the same story, since the toxin blocks acetylcholine release in the gut as well as at the muscle. Central causes still account for most hypotonia in infants (Peredo 2009). Sepsis and metabolic crises therefore stay on the list in parallel, and a floppy baby who is feeding poorly is treated as a sick baby from the start.

The trap. The commonest mistake is to call the hypotonia central simply because central hypotonia is common. Central hypotonia comes with a depressed level of consciousness, axial more than limb weakness, and normal or brisk reflexes (Peredo 2009). This baby is awake and following faces, with weakness that fatigues. The level of alertness is the single most useful fork in the floppy infant, and here it points to the periphery.

Where, when, what: "Neuromuscular junction, acute over days in a previously normal infant, most likely infant botulism, with sepsis and metabolic crisis excluded in parallel."

Where. You probably had the localization before you touched him, because watching a child get up from the floor is the most efficient examination in pediatric neuromuscular medicine. A Gowers maneuver means proximal hip weakness. Add symmetric girdle weakness, normal sensation and no fasciculations, and the motor unit narrows to muscle or the anterior horn cell. The calves decide between the two, since calf enlargement, lumbar lordosis, a waddling gait and toe walking together point to a dystrophy (Brazis 2011, p. 13).

When. The course runs over months to years and has to be read through development. He walked late and has fallen steadily further behind his friends without ever losing a skill. In a toddler, slow progression of this kind often looks like a developmental delay that is not catching up.

What. Duchenne muscular dystrophy heads the list, with Becker, its milder relative, beside it. The maternal uncle who needed a wheelchair as a teenager suggests an X-linked pattern, which supports what the examination found. Spinal muscular atrophy also produces proximal weakness and a Gowers sign, so it stays on the list until the creatine kinase level, which is very high in Duchenne, answers the question.

The traps. Toe walking nearly sent this boy to orthopedics. It is also a feature of spastic diplegia and of idiopathic toe walking (DeMyer, p. 338), and the rest of the examination decides among them. Brisk reflexes and increased tone point to the upper motor neuron, a Gowers maneuver and big calves point to muscle, and only a completely normal examination allows the idiopathic label. A second trap is ordering the creatine kinase as an afterthought. In a boy who walks late and falls, it is a simple test that can save a long diagnostic journey.

Where, when, what: "Muscle, chronic since early childhood, most likely a dystrophinopathy, so check creatine kinase and then dystrophin genetics." See the Neuromuscular section.

Where. Weak legs could come from many places, and the reduced reflexes might have tempted you toward the periphery. A sensory level on the trunk, though, almost always means the cord (Brazis 2011, p. 104), and early urinary retention agrees with it. The upgoing toes settle the matter. They show that the reflexes are reduced by spinal shock from an acute, severe lesion of the cord rather than by a peripheral lesion (DeMyer, pp. 273-274). As she recovers from the spinal shock, her reflexes should return and then become brisk.

When. The illness has evolved over hours to days, starting ten days after an infection, with back pain at the onset.

What. Order the list by danger as well as likelihood. A compressing epidural abscess, hematoma or tumor is less likely than inflammation, but delay makes its damage permanent, so urgent imaging excludes it first. Transverse myelitis fits the tempo and the preceding infection. Last week's blurred vision is easy to miss. Together with an afferent pupillary defect, it suggests optic neuritis. Optic neuritis with myelitis points toward MOG antibody disease or neuromyelitis optica spectrum disorder, the first being the more common in children, and that changes both the testing and the treatment.

The traps. The first is imaging only at the level found on the skin. The sensory level can sit several segments below the actual lesion, especially with lesions outside the cord (Brazis 2011, p. 104). A T10 level on the skin therefore does not mean a T10 lesion, and the whole spine needs imaging. The second is Guillain-Barré syndrome, which is easy to suspect when weak legs and reduced reflexes follow an infection. Guillain-Barré rarely produces a sensory level or early retention, and it does not cause upgoing toes.

Where, when, what: "Spinal cord, acute over a day after an infection, with recent optic neuritis, so compression is excluded first and then transverse myelitis is pursued with antibody testing for neuromyelitis optica spectrum and MOG antibody disease."

Where. Ataxia counts as cerebellar only once weakness and sensory loss have been excluded, because both can make a child unsteady. In this boy strength, reflexes and the plantar responses are normal. His unsteadiness therefore reflects a failure of coordination in the cerebellum or its connections. A wide-based, staggering gait with only mild overshoot of the limbs points to the midline, because disorders of the midline cerebellum affect the trunk and balance most (Brazis 2011, p. 411).

When. He became ataxic overnight, ten days after a viral illness with a rash.

What. Post-infectious acute cerebellar ataxia is the commonest cause in a well, alert young child, and it is the diagnosis here. The list still has to carry two others. A toxic ingestion belongs on the list for any toddler with acute ataxia, however carefully the house was checked. Opsoclonus-myoclonus-ataxia can begin with ataxia alone, before the chaotic eye movements, the jerks and the irritability appear. It matters because it sends you looking for a neuroblastoma.

The traps. The first is ordering imaging, or offering reassurance, without reading the clock. A posterior fossa tumor is the fear behind every ataxic child, but tumors evolve over weeks, usually with headache, morning vomiting or papilledema. An overnight onset in a cheerful child with sharp discs fits poorly, and what should change your mind is ataxia that persists or worsens. The second is examining the eyes only once. Opsoclonus may be absent on the first day, so plan a second look in a few days with that question in mind.

Where, when, what: "Cerebellum, midline, acute overnight after a viral illness, most likely post-infectious acute cerebellar ataxia, with ingestion screened and a review planned to look for opsoclonus and myoclonus."