Nocturnal Penile Tumescence Testing

Nocturnal penile tumescence testing records erections that occur during sleep, to separate psychological from organic erectile dysfunction. Healthy men have 3 to 6 erections each night, lasting 20 to 40 minutes, linked to rapid eye movement sleep, and independent of sexual thoughts. If the nerves, arteries, veins and erectile tissue are intact, these erections occur even when the man cannot achieve an erection while awake.

A recording device is placed on the penis for one to three nights. Two loops, one at the base and one at the tip, measure changes in circumference (tumescence) and the force needed to bend the shaft (rigidity). The most used system is a portable ambulatory device that is worn at home, with sleep recorded by electroencephalography in a sleep laboratory in more complete studies.

A simple screening version uses a stamp ring or a snap gauge band, which breaks when an erection occurs. The test is non-invasive and takes the whole night.

Penile tumescence testing was widely used to distinguish psychogenic from organic erectile dysfunction, but it has largely been replaced by history, examination, hormone tests, and penile Doppler ultrasound after injection of a vasoactive drug.

It remains useful in cases where the cause is unclear, in medico legal assessment, before penile prosthesis surgery, and in men with suspected psychogenic dysfunction who have not responded to treatment. In men with psychogenic erectile dysfunction, normal erections occur at night, while a normal study excludes a major vascular or neurological cause in about 90% of cases.

Indications.

• Erectile dysfunction of uncertain cause, when history and other tests do not separate organic and psychogenic types.
• Sudden onset dysfunction with preserved morning erections, to support a psychogenic cause.
• Before penile prosthesis surgery or other invasive treatment, to document the physiology, and in medico legal cases.
• Men who have failed first line drug treatment, to look for an organic cause.
• Assessment after pelvic surgery, trauma, radiotherapy, or spinal injury, when function is in doubt.
• Research and assessment of sleep related disorders, including sleep related painful erections and priapism.

Not indicated as a routine test in all men with erectile dysfunction, since most are assessed by history, examination, glucose, lipids, testosterone, and a first course of treatment.

Contraindications and precautions.

• No absolute contraindications.
• Poor sleep (sleep apnoea, insomnia, shift work, alcohol and sedative use, depression) reduces rapid eye movement sleep and erections, and can cause a false abnormal result.
• Skin irritation or allergy to the loops, and a penile condition that makes loops unsafe (Peyronie plaque with pain, local infection, priapism risk).
• Men who take antidepressants, antipsychotics, beta blockers, alcohol, or other drugs that lower nocturnal erections: medicines are reviewed.
• Recent heavy drinking or drug use.
• Patients with sickle cell disease: caution because of the risk of priapism.

Preparation and technique.

The patient is asked to keep the usual sleep routine, avoid alcohol and sedatives the evening before, and sleep in a quiet room. A loop is placed at the base and one near the corona, and the device is switched on at bedtime. The device logs the circumference and rigidity changes during the night.

Men sleep for at least 6 to 8 hours, and at least two nights are recorded, since the first night in a strange setting often has fewer erections. A sleep diary notes when the patient woke, any events, and subjective erections.

In a laboratory study, electroencephalography, eye movements and chin muscle activity are recorded to define sleep stages, and airflow is monitored when sleep apnoea is suspected.

Normal appearances.

An adult man has 3 to 6 erection episodes a night, each lasting about 20 to 40 minutes, with a total erection time of 90 to 120 minutes or more. The circumference increase is at least 3 cm at the base, and 2 cm at the tip, and the rigidity is over about 70 to 80% at the tip for at least 10 minutes. Healthy men often wake with an erection. Erections fall with age, and values in older men are lower.

Interpretation.

• Normal tumescence and rigidity: the erectile mechanism is intact, and the daytime dysfunction is likely to be psychogenic, performance related, or situational.
• Absent or reduced erections with normal sleep: organic erectile dysfunction (vascular, neurogenic, endocrine, drug related or tissue related).
• Good circumference change with poor rigidity: suggests venous leak or structural change in the erectile tissue.
• Poor tumescence at the tip and good at the base: arterial insufficiency is possible.
• Fewer erections with short sleep or poor sleep stages: the result is unreliable, and the study is repeated after the sleep problem is treated.
• Reduced erections in depression, sleep apnoea, hypogonadism, alcohol use, and with some medicines can be reversible.
• The findings are combined with penile Doppler ultrasound, hormone tests, and a neurological and vascular assessment.

Critical values and findings needing immediate action.

• There are no emergency values.
• Prolonged painful erection (over 4 hours) during the night or on awakening: urgent assessment for priapism, particularly in sickle cell disease or those who use injections.
• Findings suggesting a neurological lesion (loss of sensation, bladder and bowel symptoms with absent erections): urgent neurological assessment.
• Severe sleep apnoea found on the recording: referral for sleep medicine.

Limitations and artefacts.

• The first night effect, poor sleep, alcohol, sedative drugs, and anxiety lower erections and cause false abnormal results.
• Loops that are loose or badly placed, movement and skin contact cause false readings, and snap gauge bands do not show rigidity or duration.
• The device cannot tell whether the man can have intercourse. Daytime function depends on psychological, relationship and situational factors that nocturnal erections do not test.
• Reference ranges vary with age, and a normal result does not exclude partial vascular disease.
• Antidepressants, antipsychotics, antihypertensives, and opioids reduce erections, so a drug effect can be mistaken for disease.
• The test is time consuming, is expensive in laboratories, and is not available widely.

Special groups.

• Young men with sudden onset erectile dysfunction and preserved morning erections: a normal study supports a psychogenic cause, and counselling and psychological treatment are the main steps.
• Men with diabetes, vascular disease or after pelvic surgery: reduced erections are common, and the test is used in selected cases, with penile Doppler studies.
• Men with sleep apnoea: treatment of the sleep disorder can restore nocturnal erections.
• Men before prosthesis surgery: documenting the organic cause supports the decision.
• Medico legal cases: a full laboratory study with sleep staging is needed for reliable evidence.
• Regions: laboratory studies are rare, and the main tools are history, morning erections, examination, glucose, lipids, testosterone, and simple stamp or snap gauge bands. A history of firm morning erections is a useful, free pointer to a psychogenic cause. Cultural attitudes and stigma make men delay seeking help, and sensitive counselling matters.

Follow up tests.

• Penile Doppler ultrasound after intracavernosal injection of a vasoactive drug.
• Fasting glucose, glycated haemoglobin, lipid profile, and renal and liver function.
• Morning total testosterone, with repeat and free testosterone as needed, and luteinising hormone, prolactin and thyroid tests.
• Neurological examination, bulbocavernosus reflex, and spinal imaging when indicated.
• Sleep study (polysomnography) for sleep apnoea.
• Review of medicines, alcohol and drug use.
• Psychological and relationship assessment, and cardiovascular risk assessment.