Classification of neurasthenia

Although the diagnostic concept fell into disrepute in the English-speaking world in the 20th century (being seen more simply as a variant of depression or anxiety), it persisted in most non-English speaking countries. Consequently, the ICD-10 (World Health Organization (WHO), 1992) contains a clear definition of the concept and the World Psychiatric Association (WPA) has promoted a renewed diagnostic and research effort (WPA, 1999). In doing so, the WPA sought to broaden the concept to include cognitive, emotional, somatic, energy and sleep variables that could give the syndrome specific attributes that are clearly different to the symptoms of depressive and anxiety disorders (WPA, 1999).

The ICD-10 diagnostic criteria for research (WHO, 1993) are included in the chapter on ‘Neurotic, stress-related and somatoform disorders’ in a subsidiary section entitled ‘Other neurotic disorders’, implying a disorder of uncertain lineage. The diagnostic criteria for neurasthenia can be summarised as follows:

1. (a) either, persistent and distressing feelings of exhaustion after minor mental effort or persistent and distressing feelings of fatigue after minor physical effort;

2. (b) accompanied by one or more of the following symptoms: muscular aches or pains; dizziness; tension headache; sleep disturbance; inability to relax; and irritability;

3. (c) inability to recover through rest, relaxation or enjoyment;

4. (d) duration exceeds 3 months;

5. (e) does not occur in the presence of organic mental disorders, affective disorders or panic or generalised anxiety disorder.

Although the WHO thought neurasthenia sufficiently different to other ‘Neurotic, stress-related and somatoform disorders’ to justify its own category, research groups have tended to be more conservative. Traditionally, most psychiatric epidemiologists highlight the comorbidity with depressive and anxiety disorders (Reference WesselyWessely, 1990) and have rejected the utility of differentiating the concept until social covariates, course or response to treatment distinguish it from (say) dysthymia (Reference Goldberg, Bridges, Gastpar and KielholzGoldberg & Bridges, 1991). Such disorders have not been included in the major North American epidemiological studies of the past decade (Reference Kessler, McGonagle and ZhaoKessler et al, 1994). A more proactive view, however, has argued for evidence of independence from depression and anxiety at the levels of multivariate modelling of symptom data (Reference Gillespie, Kirk and HeathGillespie et al, 1999), genetic vulnerabilities (Reference Hickie, Kirk and MartinHickie et al, 1999a), longitudinal course (Reference Hickie, Koschera and Hadzi-PavlovicHickie et al, 1999b) and treatment response. Although such studies link neurasthenia more closely with other somatoform disorders, there is evidence that the category can be distinguished from entities such as fibromyalgia, irritable bowel, somatic depression and somatic anxiety (Reference Kirmayer, Robbins, Kirmayer and RobbinsKirmayer & Robbins, 1991).

Although the nosological debate is complex, studies in primary care indicate that prolonged fatigue syndromes are common. Prevalence rates for prolonged fatigue (typically greater than 1 month) vary from 18 to 37% (Reference Pawlikowska, Chalder and HirschPawlikowska et al, 1994; Hickie et al, Reference Hickie, Hooker and Hadzi-Pavlovic1996, Reference Hickie, Davenport and Naismith2001a), whereas the WHO Primary Care Study (Reference Sartorius, Üstün and Costa e SilvaSartorius et al, 1993) found that an average of 5.3% of general practice patients met criteria for neurasthenia (range 1.1-10.5%). All studies have emphasised that the syndrome is associated with disability, chronicity, comorbidity and high service utilisation. The Australian National Survey of Mental Health and Wellbeing (Reference Andrews, Henderson and HallAndrews et al, 2001) is the first national community based psychiatric survey to include a module specifically designed to identify people who met criteria for ICD-10 neurasthenia. This paper is an account of the key findings, emphasising not only prevalence rates but also patterns of comorbidity, disability and health care utilisation.

Sample

The national survey was conducted by the Australian Bureau of Statistics under the terms of their Act that guarantees the privacy of respondents. A multi-stage sample of private dwellings in rural and urban Australia was drawn. Each state and territory was stratified and each dwelling within a stratum had an equal and known probability of selection. In all, 13 624 private dwellings were initially selected in the survey sample, and one adult member aged 18 years and over randomly selected as the possible respondent. A total of 10 641 people participated, a response rate of 78.1%. The age and gender characteristics of the sample were weighted to match the age and gender distribution in the national census.

Assessment

The whole interview was administered from a laptop computer. The Composite International Diagnostic Interview (CIDI v 2.1; WHO, 1997) was used to determine, using ICD-10 criteria, the presence of seven anxiety disorders, three affective disorders and four substance use disorders in the 12 months prior to interview.

Neurasthenia was identified using an interview developed by Tacchini et al (Reference Tacchini, Janca and Issacs1995). All results in this paper are with the exclusion criteria not applied for other mental or physical disorders. Personality disorders were identified using a screening questionnaire (Reference Loranger, Janca and SartoriusLoranger et al, 1997).

Disability was measured at the beginning of the interview by the SF-12 (Reference Ware, Kosinski and KellerWare et al, 1996) and by the National Comorbidity Survey ‘days out of role’ questions. Neuroticism was measured using the 12-item version of the Eysenck scale (Reference Eysenck, Eysenck and BarrattEysenck et al, 1985). Demographic and service utilisation data were also obtained. The method of the survey has been described previously (Reference Andrews, Henderson and HallAndrews et al, 2001).

Data analysis

Routine data analysis procedures were used but, as a result of the complex sample design and weighting, specific software was required to estimate standard errors (s.e.). The s.e. of prevalence estimates and confidence intervals around odds ratios (ORs) derived from logistic regression models were estimated using delete-1 jackknife repeated replication in 30 design-based subsamples (Reference Kish and FrankelKish & Frankel, 1974). These calculations used the SUDAAN software package (Reference Shah, Barnwell and BieglerShah et al, 1997).

Diagnosis

The criteria for neurasthenia are listed above. Criterion A, prolonged and excessive fatigue, was endorsed by 1465 people (13.2% of the sample). These responses were probed to ensure that the symptom was clinically significant and not attributed by the respondent to drugs or alcohol, physical illness or injury (601 persons agreed that this was so). Criterion C requires that the fatigue does not respond to rest and 318 of the 601 participants endorsed this. Criterion D requires that the fatigue lasts 3 months or more, and this was so for 186 participants. Finally we asked about the presence of the Criterion B symptoms, 172 of the 186 met this criterion. Thus, although complaints of fatigue are common, only one in nine people who complain of fatigue meet current ICD-10 criteria for neurasthenia. As distinct from non-specific complaints of fatigue, neurasthenia is not a common mental disorder.

Prevalence

Data on the weighted prevalence of neurasthenia are displayed in Table 1, by age and gender, for people meeting criteria in the past month (1.2%) and sometimes in the past year (1.5%). Only 20% of people who met criteria during the year were not current cases. The disorder is chronic. The female to male ratio was small (1.4 and 1.2) in contrast to what is often believed, and different from the pattern seen in health care facilities. On further examination of the numbers of people in the population who reported fatigue (13.2%), significantly more females than males said ‘yes’ (14.9% v. 11.3%; P<0.05). In addition, when respondents were asked whether it was clinically significant (601 said ‘yes’), female rates were still higher but the confidence intervals just overlapped (6.3% v. 4.4%; P>0.05). For all other criteria (B-D) the rates of endorsement were almost identical for males and females. Thus, although more women than men in the population report fatigue the prevalence of neurasthenia is not higher in women. The multivariate associations of demographic variables are shown in Table 2 together with those for people with any 12-month mental disorder. Both sets of disorders decline with age, both are more common among people who are separated, widowed or divorced, both are more common among those with less education and both are more common among those born in Australia. That is, as the socio-demographic characteristics of neurasthenia are similar to other mental disorders, it is likely that social risk factors are shared. Employment is not significant in neurasthenia, whereas psychological morbidity generally is associated with not being in the labour force.

Table 1 Weighted prevalence of 12— and 1-month ICD-10 neurasthenia by age and gender

Age	12-month			1-month
	Males	Females	Persons	Males	Females	Persons
	% (s.e.)	% (s.e.)	% (s.e.)	% (s.e.)	% (s.e.)	% (s.e.)
18-24	1.0 (1.2)	2.4 (0.9)	1.7 (0.7)	1.0 (1.2)	1.6 (0.7)	1.3 (0.7)
25-34	1.1 (0.4)	1.8 (0.4)	1.5 (0.3)	0.7 (0.4)	1.5 (0.4)	1.1 (0.3)
35-44	1.6 (0.3)	1.7 (0.6)	1.6 (0.3)	1.4 (0.3)	1.2 (0.6)	1.3 (0.3)
45-54	1.8 (0.5)	2.8 (0.7)	2.3 (0.4)	1.7 (0.6)	2.1 (0.5)	1.9 (0.4)
55-64	0.8 (0.4)	1.1 (0.5)	1.0 (0.4)	0.8 (0.4)	1.1 (0.5)	1.0 (0.4)
> 65	0.7 (0.4)	0.5 (0.2)	0.6 (0.2)	0.7 (0.4)	0.3 (0.2)	0.5 (0.2)
Total	1.2 (0.3)	1.7 (0.3)	1.5 (0.2)	1.1 (0.3)	1.3 (0.2)	1.2 (0.2)

Table 2 Multivariate associations of socio-demographic correlates for 12-month neurasthenia and any 12-month ICD—10 mental disorder

Correlates1	ICD—10 mental disorder
	12-month neurasthenia		Any 12-month mental disorder2
	Odds ratio	95% CI	Odds ratio	95% CI
Age
18-24	1.0	—	1.0	—
25-34	1.0	0.4-2.9	1.0	0.8-1.3
35-44	1.1	0.3-4.3	1.0	0.8-1.2
45-54	1.6	0.5-4.8	0.8	0.6-1.1
55-64	0.4*	0.2-1.0	0.4**	0.3-0.6
> 65	0.4	0.1-1.8	0.2**	0.1-0.2
\batchmode \documentclass[fleqn,10pt, legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \({\chi}_{5}^{2}(P)\) \end{document}	17.7	0.003	218.5	<0.001
Marital status
Married/de facto	1.0	—	1.0	—
Separated/divorced/widowed	2.4*	1.5-3.7	2.0**	1.5-2.5
Never married	1.2	0.6-2.3	1.5**	1.3-1.8
\batchmode \documentclass[fleqn,10pt, legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \({\chi}_{2}^{2}(P)\) \end{document}	14.4	0.001	48.9	<0.001
Education
Bachelor degree or higher	1.0	—	1.0	—
Diploma	0.8	0.2-4.2	1.2	0.9-1.6
Vocational qualification	1.9	0.6-6.2	1.5*	1.1-2.0
High school only	2.3	0.6-8.1	1.6**	1.3-1.8
\batchmode \documentclass[fleqn,10pt, legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \({\chi}_{3}^{2}(P)\) \end{document}	7.9	0.048	36.3	<0.001
Employment
Employed (f/t or p/t)	—	—	1.0	—
Short-term unemployed3	—	—	1.6*	1.1-2.3
Long-term unemployed4	—	—	2.6**	1.8-3.8
Not in the labour force	—	—	1.6**	1.3-1.9
\batchmode \documentclass[fleqn,10pt, legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \({\chi}_{3}^{2}(P)\) \end{document}	—	NS	38.5	<0.001
Country of birth
Australia	1.0	—	1.0	—
Other English speaking country	0.5	0.2-1.0	0.9	0.7-1.2
Other non-English speaking country	0.6	0.3-1.1	0.8*	0.6-1.0
\batchmode \documentclass[fleqn,10pt, legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \({\chi}_{2}^{2}(P)\) \end{document}	6.6	0.037	6.6	0.037

Comorbidity is regarded as a hallmark of neurasthenia. In Table 3 we present data on the prevalence of comorbid disorders among people with neurasthenia. In Model 1 we show that there is more comorbidity with major depression, panic disorder and generalised anxiety disorder than could be expected by chance after adjustment for the prevalence of the comorbid disorder and the average level of comorbidity of that disorder. These are the disorders specified as exclusion criteria in ICD-10. In Model 2 we calculate the same information, not for individual disorders but for disorder groups. Now the significant associations are with affective, anxiety and personality disorders. Naturally the association with any mental disorder is significant, as is the association with any self-reported physical disorder. People who meet criteria for neurasthenia report symptoms that suggest they are at increased risk for specific mental and any physical disorder. Their risk of a substance misuse disorder is not increased.

Table 3 Weighted prevalence and odds ratios of comorbid ICD—10 mental disorders and any physical disorder among persons with 12-month neurasthenia

Comorbid disorder1	Prevalence of disorder among persons with 12-month neurasthenia
	% (s.e.)	OR1(95% CI)
Model 1: Individual disorders
Major depression	50.4 (4.6)**	5.2 (3.0-9.0)
Dysthymia	14.6 (2.7)	1.5 (0.7-3.2)
Panic with or without agoraphobia	27.8 (3.9)*	2.6 (1.4-4.9)
Social phobia	19.0 (4.8)	2.2 (0.8-6.3)
Generalised anxiety disorder	40.4 (4.6)*	2.7 (1.3-5.4)
Obsessive—compulsive disorder	3.1 (1.9)	0.7 (0.2-2.2)
Post-traumatic stress disorder	27.5 (8.5)	2.7 (0.8-9.5)
Alcohol misuse or dependence	14.0 (3.3)	0.8 (0.4-1.6)
Drug misuse or dependence	10.0 (2.4)	2.0 (0.9-4.6)
Model 2: Disorder groups
Any affective disorder	53.7 (4.4)**	5.2 (3.3-8.1)
Any anxiety disorder	64.9 (4.3)**	6.6 (4.2-10.6)
Any substance use disorder	19.9 (4.1)	1.1 (0.5-2.1)
Any personality disorder	35.5 (4.7)*	2.0 (1.2-3.5)
Model 3: Any other mental disorders	79.3 (4.8)**	14.4 (7.9-26.5)
Model 4: Any physical disorder2	62.3 (4.4)**	2.7 (1.8-4.0)

When comorbidity is endemic it is difficult to know whether the attribute being measured belongs to the target disorder or to the comorbid disorder. In clinical practice, when the patient has more than one disorder, the patient and doctor agree on a priority and usually deal with the main problem first. In the survey, after all disorders had been enumerated, we listed the groups of symptoms they had complained of, and asked people who had met criteria for more than one disorder: ‘Which of these problems troubles you the most?’. We regarded this as the patient's main problem. In 13 people neurasthenia was the only disorder present, whereas a further 36 who did have comorbid disorders, identified neurasthenia as their main problem. Thus, neurasthenia was the main problem in 49 people (less than 0.5% of the population). Of the remainder of people with neurasthenia and comorbid disorders, 50 nominated an affective disorder as their main problem, 39 an anxiety disorder and 31 a physical disorder as their main problem. Three people thought personality or substance misuse disorders were their main problem.

In Table 4 we present data on neuroticism, disability measured by the SF-12 and by disability days, and service utilisation in terms of consultations and hospital admissions. People with neurasthenia as a main problem were less likely to be comorbid with a mental or a physical disorder, less disabled and used fewer services than the complete group. We then examined all people with neurasthenia, divided into those with neurasthenia as a main problem and those with neurasthenia who identified affective, anxiety or physical disorders as their main problem. People with neurasthenia as a main problem were less disabled (P=0.026) and used fewer services (P=0.005) than did the other three groups.

Table 4 Chronicity, neuroticism, disability and health service utilisation among all persons with 12-month neurasthenia, those with neurasthenia as their principal complaint and among those with an anxiety, affective or a physical disorder as their principal complaint

	12-month neurasthenia1
	All 12-month neurasthenia (n=172)	A. Neurasthenia as main problem (n=49)	B. Affective as main problem (n=50)	C. Anxiety as main problem (n=39)	D. Physical illness as main problem (n=31)
Neuroticism, mean (s.e.)
EPQ—N	6.7 (0.3)	5.7 (0.5)	7.4 (0.8)	8.3 (0.9)	5.7 (0.6)
Disability, mean (s.e.)
SF-12 mental component score	36.4 (1.1)	42.5 (1.5)	31.4 (2.7)*	34.3 (2.5)*	36.6 (4.5)
SF-12 physical component score	40.4 (1.0)	44.7 (1.9)	42.3 (2.3)	37.6 (2.3)	33.7 (2.8)
Disability days	12.8 (1.1)	7.5 (2.4)	16.2 (2.5)	15.3 (2.2)	13.1 (3.0)
Service utilisation, % (s.e.)
Any consultation2	95.8 (2.1)	87.2 (8.0)	100 (-)	97.5 (4.0)	100 (-)
Any mental health consultation3	60.5 (4.6)	50.9 (11.9)	88.4 (4.8)*	61.2 (10.8)	38.1 (11.7)
Any hospital admission4	23.0 (3.1)	9.2 (5.6)	27.3 (7.2)	17.8 (8.2)	46.6 (14.6)*