Secondary Narcolepsy Masquerading as Obstructive Sleep Apnea.

Sir,

Secondary causes of narcolepsy are attributable to brain insults like trauma, infections, stroke, and demyelination.[12] Though the pathogenesis is unclear, current thinking proposes that the wakefulness promoting neurons of lateral hypothalamus are destroyed by autoimmune mechanisms triggered by infection, injury or vaccination.[3] There are studies that have shown associations between narcolepsy and streptococcal infections[4] or H1N1 epidemics.[5] We report a case of narcolepsy without cataplexy which developed as a consequence of probable Dengue virus infection and was initially mistaken for obstructive sleep apnea. (OSA).

A 26-year-old man presented with excessive sleepiness and lethargicness for the past one year. Symptoms were preceded by a febrile illness for which he was evaluated and diagnosed to have dengue infection based on clinical features, thrombocytopenia and serology. He made a clinical recovery over 7-10 days after which he noted progressive symptoms of excessively sleepiness. Contrast enhanced MRI brain was done to rule out possibility of encephalitis and was found to be normal. Otorhinolaryngology evaluation showed a deviated nasal septum and features of chronic sinusitis for which he underwent functional endoscopic sinus surgery (FESS). He reported no symptomatic benefit and hence an overnight polysomnography (PSG) was planned. PSG showed findings of OSA with an apnoea-hypopnea index (AHI) of 24 and REM AHI of 40. After sleep endoscopy, patient was taken up for surgical management of OSA. However, his symptoms continued to worsen which prompted a neurology review. On further interrogation, he had excessive daytime sleepiness (EDS) without events suggesting cataplexy and sleep paralysis. Overnight PSG showed an AHI of four and sleep onset rapid eye movement sleep periods (SOREMPs). Multiple sleep latency testing (MSLT) revealed SOREMPs in all the five attempts at sleep [Figure 1]. He fulfilled the DSM-5 criteria for narcolepsy and can be categorised as narcolepsy type 2 based on the ICSD-3 criteria.

Figure 1

Representative polysomnogram of the patient during MSLT showing Sleep onset REM sleep

A high index of suspicion is required to diagnose mono-symptomatic cases and incomplete presentations.[6] The presence of SOREMPs in MSLT makes the diagnosis unmistakable but this is not routinely undertaken in patients with excessive daytime sleepiness (EDS). The presence of respiratory events like apnoea and hypopnoea further distracts the treating physician from the primary disorder. The delay in diagnosis can be as high as 15 years as reported by Thorpy et al.[7] The present report highlights the high chance of misdiagnosis which can be far worse than delay in diagnosis in terms of unnecessary, expensive and at times harmful interventions the patients are subject to.

The role of infections and autoimmunity in the pathogenesis of the disorder is founded on indirect observations like temporal association with epidemics, detection of antibodies like ASO from patient sera and response to immunotherapy. The author (SSB) in a previous series of 13 patients with narcolepsy from India, did not discover any temporal association with infections or seasonal epidemics.[8] There is no reference of this aspect in the other major series from the country by Shukla et al.[9] In the wake of emerging infections and rising epidemics, this report evokes interest because of its clinical and epidemiological implications.

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Conflicts of interest

There are no conflicts of interest.