During meals, in the cinema, even partway through teaching a class: Ben found himself falling asleep no matter where he was. Review of his lifestyle failed to unearth an inner party animal that might be held responsible. Blood tests ruled out under-active thyroid or diabetes. But his score on the Epworth Sleepiness Scale was impressively dire: something was wrong.
The commonest explanation would be obstructive sleep apnoea (OSA), where heavy snoring actually halts breathing throughout the night. The resulting periods of low blood oxygen cause profound fatigue the following day, though patients think they’ve slept well. But OSA principally affects the obese. Ben wasn’t svelte – he also complained that he was putting on weight inexplicably – but his collar size was below the 17-inch threshold associated with OSA.
The only way to tell for sure would be a sleep study. Ben spent a night at the local sleep unit, wired up to all manner of monitoring equipment. There was no evidence of apnoea attacks, which ruled out OSA. The consultant there raised the possibility of narcolepsy. This affects just one in 2,500 people, and arises when brain cells producing a substance called hypocretin die off. Hypocretin plays a crucial role in regulating the sleep-wake cycle.
A different sort of study is needed to diagnose narcolepsy – a multiple sleep latency test (MSLT). This measures how swiftly someone falls asleep when napping during the day, and also charts what type of sleep they enter. People with narcolepsy zonk out at the click of a finger, and typically move straight into rapid-eye-movement (REM) sleep. Again Ben was hooked up to the monitors, but on no occasion demonstrated the characteristic immediate-REM pattern.
The consultant discharged him saying narcolepsy was excluded, and recommending I refer him to an endocrinologist in case the fatigue and weight gain indicated some obscure hormonal problem. Ben came in to discuss things, and at one point he mentioned odd episodes where his legs would buckle beneath him if he was laughing, or if he’d been surprised by something.
It rang a bell. “Did you mention that to the consultant?”
“Definitely,” he said. “I remember telling him I’d collapsed at crazy golf.”
I phoned the sleep specialist the next day. Like me, he immediately recognised that Ben was describing a second disorder, cataplexy, where a sudden emotional jolt causes a reflex loss of muscle tone in the limbs. Cataplexy, too, is related to low hypocretin levels – it often goes hand in hand with narcolepsy. The consultant got Ben back in. This time he performed a lumbar puncture – tapping fluid from around the spinal cord – and sent it for hypocretin tests. Ben’s levels were indeed very low. A rare instance of a narcolepsy sufferer who doesn’t nap straight into REM sleep.
The case reminded me of several important lessons. First, all tests can produce false results: Ben’s consultant had interpreted the MSLT as excluding narcolepsy, and his confidence in the result had led him to miss a textbook description of cataplexy. Second, we should remain healthily sceptical about other doctors’ opinions: if I’d have accepted the consultant’s verdict at face value, Ben might still be undiagnosed. Third, we should never be too proud to change our mind: as soon as the consultant realised his thinking had gone astray, he acted to put matters right.
And finally, knowledge is never complete. The consultant and I were unaware that hypocretin has recently been linked to body mass regulation. High levels stimulate “brown fat” tissue, which burns off calories; lower levels are associated with more ready weight gain. Fascinatingly, hypocretin might hold the key as to why some of us find it easier to stay slim than others.
And there is the intriguing possibility that hypocretin augmentation might represent a future treatment for obesity. Meanwhile, Ben’s narcolepsy has responded to drug therapy, and he is managing to keep himself awake once again.
This article appears in the 13 Jun 2018 issue of the New Statesman, Who sunk Brexit?