Catathrenia: Symptoms, Types, Causes and Treatment

Catathrenia, often called nocturnal groaning, is a rare and intriguing sleep disorder that remains underrecognized despite the social and clinical challenges it can cause. Characterized by unusual, sometimes alarming sounds during sleep, catathrenia can lead to confusion, misdiagnosis, and distress for both sufferers and their bed partners. This article explores the latest scientific insights into its symptoms, types, underlying causes, and treatment approaches, helping demystify this unique sleep phenomenon.

Symptoms of Catathrenia

Catathrenia presents with distinct symptoms that set it apart from more common sleep disorders like snoring or sleep apnea. Understanding these symptoms is crucial for correct identification and differentiation from other conditions.

Primary Symptom	Description	Sleep Stage	Source(s)
Groaning/Moaning	Prolonged, monotonic moan or groan during sleep	Mostly REM, also NREM	1 4 5 8 10 11
Prolonged Expiration	Extended out-breath with vocalization	Alternates with normal breathing	4 5 10 11
Sleep Disturbance	Not typically noticed by the sleeper, but disturbs bed partners	Nighttime, end of sleep cycles	1 5 9
Social Embarrassment	Emotional impact due to unusual sounds	N/A	3 9

Table 1: Key Symptoms

Groaning and Moaning During Sleep

At the heart of catathrenia is a distinctive, monotonous groaning or moaning sound that emerges during sleep. This sound is produced exclusively during exhalation and can last anywhere from a couple of seconds to nearly a minute. The sound is often rhythmic or semi-rhythmic, setting it apart from the irregular nature of snoring. Notably, these vocalizations frequently occur in clusters, particularly in the latter part of the night or during rapid eye movement (REM) sleep, but can also be seen in non-REM (NREM) stages 1 4 5 8 10 11.

Prolonged Expiratory Breathing

Catathrenia's vocalizations are always linked to a prolonged out-breath. The breathing pattern is unique: a deep inhalation is followed by a slow, noisy, extended expiration, after which a brief, forceful exhalation may occur, and then another deep inhalation. Unlike sleep apnea, there is usually no oxygen desaturation or significant daytime respiratory complaints 4 5 10 11.

Awareness and Social Impact

Most people with catathrenia are unaware they make these sounds—many discover the problem only through complaints from bed partners or family. While the disorder typically doesn't disturb the sleeper, it can cause significant distress to others, leading to embarrassment and relationship strain 3 9. Only a minority of patients report excessive daytime sleepiness as a symptom 3 5 9.

Differentiation from Other Disorders

Catathrenia is sometimes mistaken for snoring, sleep apnea, epileptic seizures, or even psychiatric conditions. However, its hallmark is the combination of vocalization with a specific breathing pattern during sleep, especially during exhalation 1 7 8 9 10.

Types of Catathrenia

Modern research indicates that catathrenia is not a single, uniform disorder but may manifest in several subtypes. These are categorized based on the timing of episodes, sound characteristics, and associated sleep stages.

Type	Sleep Stage Predominance	Sound Pattern	Source(s)
REM-type	Mainly REM sleep	Rhythmic/semi-rhythmic, vocal	5 6 8 9 11
NREM-type	Mostly NREM (N1/N2)	Shorter, semi-continuous moans	1 4 6 9
Acoustic Subtypes	Varies	Sinusoidal (monotone) or sawtooth (higher pitch)	6 7 8
Typical/Atypical	Defined by ICSD or not	Typical: classic features; Atypical: shorter/irregular	1 9

Table 2: Catathrenia Types

REM-Predominant Catathrenia

Most cases of catathrenia occur during REM sleep, and these episodes often cluster at the end of the night. REM-type catathrenia is characterized by longer, more rhythmic vocalizations and is frequently preceded by brief arousals on EEG 5 8 9 11. In a large series, 81% of catathrenia periods arose from REM sleep 5 11.

NREM-Predominant Catathrenia

Some patients experience catathrenia predominantly during NREM sleep, especially in lighter sleep stages (N1 and N2). NREM-type episodes tend to be shorter, more regular, and sometimes more frequent, but with less pronounced moaning than in REM-type 1 4 9.

Acoustic Subtypes

Sound analyses reveal at least two principal acoustic subtypes:

• Sinusoidal (Monotone): Regular, monotonic sounds with a normal fundamental frequency.
• Sawtooth (High Pitch): Higher-pitched, less regular but still rhythmic moaning 6 7 8.

These types are distinct from snoring, which has a chaotic, guttural signature and lacks the harmonics found in catathrenia 6 7 8.

Typical vs. Atypical Catathrenia

The International Classification of Sleep Disorders (ICSD) defines "typical" catathrenia with classic features. However, studies show that many patients exhibit “atypical” forms, with shorter or irregular events that don’t fully meet the criteria but are likely on the same spectrum 1 9.

Causes of Catathrenia

The exact cause of catathrenia remains elusive, but several mechanisms and contributing factors have been proposed based on clinical and physiological studies.

Factor	Description	Evidence/Notes	Source(s)
Abnormal Respiratory Pattern	Prolonged expiration with reduced breathing rate	Suggests internal respiratory drive abnormality	4 10
Vocal Cord Involvement	Sound produced by vocal cords during expiration	Confirmed by sound analyses	7 8 9
Sleep Stage/Arousal Link	Often preceded by EEG arousal, REM/NREM association	Seen in PSG studies	5 11
Airway Obstruction	Mild upper airway obstruction, sometimes co-exists with OSA	Some cases respond to CPAP	1 4 9 13
Possible Neurological Basis	Dysfunction of post-inspiratory neurons or vestigial breathing pattern	Theoretical	4 10
Medication Effects	Sodium oxybate may induce catathrenia	Observed in narcolepsy patients	12

Table 3: Causes and Mechanisms

Breathing and Vocalization Abnormalities

Catathrenia is fundamentally a disorder of breathing regulation during sleep. The characteristic pattern—deep inhalation followed by slow, groaning expiration—suggests an abnormality in the control of expiratory breathing. Unlike obstructive sleep apnea, there is no significant oxygen desaturation, but a mildly positive airway pressure at the start of expiration has been documented, hinting at partial expiratory upper airway narrowing 4 10.

The vocalizations are produced by the vocal cords, as demonstrated by acoustic analyses that identify harmonics and formants typical of laryngeal (vocal fold) sounds 7 8 9.

Neurological and Respiratory Drive Theories

Several theories have emerged:

• Internal Respiratory Drive Abnormality: Catathrenia may reflect an abnormality in the internal respiratory drive system, possibly a persistence of a neonatal or vestigial breathing pattern 10.
• Neuronal Dysfunction: Dysfunction in the post-inspiratory neurons responsible for modulating breathing rhythm may contribute 4.
• Arousal Link: Many catathrenia episodes are preceded by micro-arousals on EEG, suggesting a possible arousal-related trigger 5 11.

Role of Airway Obstruction

Some cases of catathrenia occur alongside mild upper airway obstruction or even obstructive sleep apnea (OSA). In such cases, catathrenia may improve with treatments that stabilize the airway, such as CPAP or mandibular advancement devices 1 4 9 13.

Other Contributing Factors

• Medications: Sodium oxybate, a medication used for narcolepsy, has been linked to new-onset catathrenia in some patients, indicating that certain drugs may influence respiratory patterns during sleep 12.
• Demographics: Catathrenia affects both men and women, often younger and thinner individuals, but the reasons for this demographic pattern are unclear 9 10.

Treatment of Catathrenia

Given catathrenia's unclear pathogenesis and rarity, treatment approaches are often individualized, focusing on symptom reduction and improving quality of life.

Treatment	Effectiveness	Notes/Indication	Source(s)
CPAP (Continuous Positive Airway Pressure)	Often reduces/eliminates groaning	Especially with coexisting OSA or airway obstruction	1 2 4 9 13
Mandibular Advancement Devices	Reduces atypical catathrenia	For mild upper airway obstruction	9
Surgery	Effective in select cases	Upper airway soft tissue surgery, sometimes with oral appliance	2
Pharmacotherapy	Limited evidence	Sleep-consolidating agents may help some	5
Behavioral Approaches	Reassurance, education	For social/psychological impact	3 9

Table 4: Treatment Approaches

CPAP: The Mainstay of Treatment

Continuous Positive Airway Pressure (CPAP) is the most commonly reported and studied intervention for catathrenia, especially when there is evidence of airway obstruction or overlap with sleep apnea. Studies show that CPAP can reduce or eliminate groaning episodes in many cases, although not universally. In one series, CPAP reduced events by an average of 75%, and in others, it resolved groaning entirely 1 2 4 9 13.

Oral Appliances and Surgery

For patients who cannot tolerate CPAP or have documented upper airway narrowing, mandibular advancement devices or selected soft tissue surgeries (such as uvulopalatopharyngoplasty) have been used successfully. These interventions are especially helpful in atypical catathrenia or when there is mild airway obstruction 2 9.

Pharmacological and Behavioral Approaches

Sleep-consolidating medications (e.g., clonazepam) have shown limited benefit, mostly in patients with associated sleep fragmentation or arousal disorders 5. However, long-term adherence to pharmacotherapy or CPAP may be poor.

Education, reassurance, and addressing the social impact remain important, as catathrenia is not dangerous and often more distressing to bed partners than to the patient themselves 3 9.

Addressing Medication-Induced Catathrenia

When catathrenia emerges as a side effect of medications like sodium oxybate, careful assessment and individualized management are warranted. Withdrawal of the offending drug is not always necessary if the condition is benign and not causing significant distress 12.

Conclusion

Catathrenia is a rare but fascinating sleep disorder that demands careful recognition and nuanced management. While its exact cause is still under investigation, advances in polysomnography, acoustic analysis, and airway physiology have helped clarify its features and guide treatment.

Key points:

• Catathrenia is characterized by prolonged, rhythmic groaning or moaning during expiration, most often in REM sleep, but also in NREM stages.
• It has several types, varying by sleep stage, sound pattern, and adherence to classic diagnostic criteria.
• The disorder likely arises from abnormal respiratory control and vocal cord involvement, sometimes with a contribution from mild airway obstruction or neurological factors.
• Treatments such as CPAP, mandibular advancement devices, and surgery can be effective, particularly when airway obstruction is present, but reassurance and education are also vital.
• Catathrenia is benign for the sleeper but can cause significant social and relationship stress, highlighting the need for empathy and comprehensive care.

With ongoing research, our understanding and management of catathrenia will continue to improve, offering hope and solutions for those affected by the "sirens of the night."