The Neuroscience of Brown-Séquard Syndrome: is Katya Inhibiting Josh's Recovery?

Given that my doctoral training is in neuroscience, I am always delighted when some neurological condition turns up in a book. For a detective series written by a non-scientist, the Cormoran Strike books have been an amazingly rich source, with phantom limb syndrome, BIID, and even a brief mention of Capgras syndrome.  

So it was exciting to see that Brown-Séquard syndrome was featured in The Ink Black Heart.  But how accurate is it?  Does it alone account for the symptoms Josh Blay has? And how do you wind up paralyzed on one side and without feeling on the other, anyway?

First, yes, Brown-Séquard syndrome is a thing, though is is very rare, happening in less that 4% of all spinal cord injuries. It was first described by Charles Éduoard Brown-Séquard in 1850. Brown-Sequard, a figured well-known in my own sub-field of hormones and behavior,  had highs and lows in his career. He is often remembered for some now-discredited self-experiments he performed late in life, claiming that an extract from animal testicles that he self-administered increased his physical strength, mental acuity and the length of his urine stream. However, he would perhaps be more fairly remembered for two earlier contributions. First, his work with the adrenal glands provided some of the first evidence for the existence of hormones: a tremendously important discovery that help launch the field of endocrinology. Second, his research on spinal cord anatomy showed that different modalities are carried by different tracts in the cord, and led to the description of the syndrome that now bears his name. 

Brown-Séquard syndrome produces its odd collection of symptoms because it involves a hemisection of the spinal cord: in other words, a cut through half of it. The first thing to understand is that different parts of the cord carry different sensory and motor signals. Fibers that carry motor commands from brain to muscle travel in the lateral corticospinal tract (see blue on picture to the left). Fibers that carry pain and temperature signals from skin to brain travel in the spinothalamic tract (red). And fibers that carry information about vibration, pressure and limb position (which is very important for reaching for objects, walking, etc) are carried in the posterior column (green). 

You have probably heard that the right half of the brain controls the left half of the body and vice versa. This is true. When you move your right hand, the command originates in your left motor cortex. If you are touched on your left leg, the sensory signals will be sent to your right somatosensory cortex. But, there is a difference in where different signals cross to the opposite (or contralateral) side of the body. If you press on your right big toe, the sensory signals from your toe travel to the lower spinal cord, and go up the cord on the right side, in the posterior column, until they reach the brain stem, where they cross over to the left side, and are relayed to the left sensory cortex (left diagram, above).  If you stick a pin in your right toe, however, the pain signals get carried to the lower spinal cord, cross over to the left side there, and travel up through the left spinothalamic tract (right diagram). Your motor signals (not pictured) follow the same basic path as the vibration/pressue/position signals. If you decide to wiggle your right toe, the command starts in the left motor cortex, crosses to the right side at the midbrain, and travels down to the lower cord in the right lateral corticospinal tract. 

If you sever the full spinal cord, you will, of course, lose all pain and sensation below the site of the break. This could well have been Josh Blay's fate if his jacket collar had not impeded the machete blade. But, if only the left half the cord is cut, as in the yellow on the first figure above, the damaged posterior column and lateral corticospinal tract will be carrying signals from the left side of the body. The severed spinothalamic tract is carrying informations from the right side of the body. Therefore, the patient loses position/vibration information  and motor control from the same side as the cut, and pain and temperature sensation from the opposite side of the cut. Here's a nice video that explains it even better:

So, is Josh Blay a medically accurate depiction of a Brown-Séquard patient?  Partially. The basic premise is right: paralyzed on one side, loss of sensation on the other. As his arms were affected, the injury must have been pretty high in the neck, probably around the cervical 4 or 5 (C4 or C5) vertebra. 

But there are some things hard to understand. First, Josh received two stab wounds on February 12: one in the back that punctured a lung, and one in the neck that was partially stopped by his jacket collar. Katya Upcott tells Strike that Josh has Brown-Séquard on April 8th. At that time, Josh was supposedly still struggling to talk, and Strike tells Sara Niven on May 14th that he had only recently regained the ability to speak. This is strange; how did Josh dictate the letter to put in Edie's coffin, given that her funeral was presumably only a week or so after her death?  

Second, Brown-Séquard itself would not be expected to cause speech problems, as vocal movements are controlled by cranial nerves, which are above the spinal cord, up in the brainstem. The stab wound in the back probably did extensive lung damage, and it is likely that either the back or the neck wound did damage to the trachea, since Josh had a "healed tracheostomy scar" visible at the base of his throat. That may account for the difficulty talking,  especially if he had to be placed on a ventilator immediately after the injury, although that still would not explain how he could dictate the coffin letter. 

But the most difficult part is explaining why Josh describes his symptoms this way on Strike and Robin's mid-May visit. 

‘Yeah... I can feel stuff on the side tha’s paralysed. Bu’ the side I can move is numb. Can’ feel nuthin’. The doctors say it migh’ improve a bit, but I’ll never... never go back to normal...'

As we have seen, that is not exactly right. Josh would be able to feel pain and temperature sensations from his paralyzed side, but not vibration, light pressure or a sense of where his limbs were. He would, however, be able to feel all of those sensations on his non-paralyzed side, so it would not be entirely numb. Worse, Josh is acting like a person who is completely paralyzed. Even with loss of pain and temperature, he should have the tactile feeling needed to use his mobile arm and hand for at least some tasks, like picking up a cup to drink and and a tissue to wipe his nose. 

Of course, if he could do that, we would not have gotten the touching scene of Strike helping him, so...

Josh should also feel more optimistic about his recovery. As far as spinal injuries go, Brown-Séquard has one of the best prognoses for recovery, with 90% of patients recovering bowel, bladder and sexual function, and most regaining the ability to walk walk with no or minimal aids (i.e., a cane, not a wheelchair). He may not ever have the fine motor skills needed to return to his animation work, and recovery could take a year or longer, but, with treatment, a patient like Josh would be expected to be able to care for himself and live independently. Indeed, a lot of the recovery takes place in the first two months after the injury. 

Therefore, three months after the attack, it is a little hard to see why Josh has not made more progress. It is possible the lung injury incapacitated him for some time and he has not been able to get the physical rehabilitation he needs. He might be suffering from severe depression or other emotional problems and not able to cooperate with treatment at this time. But I'm wondering if Katya's daily visits and ministrations are excessive, exacerbating his helplessness and actively discouraging him from trying to learn to do more for himself. Strike certainly questions her emotional attachment to him, which seems stronger than for her own daughter. It might be better for Josh if she wasn't so attentive. 

It would not shock me if Josh's rate of recovery picked up substantially after Gus is caught, not just because of the emotional lift it will give hm to see Edie's killer brought to justice, but because Katya, recovering from her own stab wounds, will not be able to foster dependency. Honestly, I am hoping the Widow Upcott gets a nice long hospital stay. And, as an added bonus, Flavia can go live with her auntie and the puppies. She's certainly earned a break from that dreadful home.