Monday, April 7, 2014

Utilitarian aspect of learning disorders

Looking into the classification of learning disorders we can see a huge inequality between learners who had specific learning disorders. What I am saying is not that people who are dyslexic are put into more difficult situation compared with the "normal" crowd, but rather that people with a less recognized learning disorder such as dyscalculia are essentially labeled as "retarded" or "stupid" in general, whereas people with a more recognized disorder (even though it is less well-defined) such as dyslexia receive a lot of aid (in fact more so that they sometimes fare better than an average student)... when in fact that they both have deficit in one and only one domain of learning. This, sir, is extremely unfair.

I believe that dyslexia receive so much attention because number one, the alleles related to it probably co-segregates with a lot of high-fitness (as in, evolutionarily, intelligent, beautiful, sociable, and so on) alleles -- and parents of these children tended to be well-off, better educated, and at a better position to fight for resources for their children. and number two, dyslexia is interesting to researchers because these children fails only in one aspect of language development, and there are knowledge to be found in this area[1].

I believe that, care for these developmental disorders would improve if we could define a model in which a child can be scored, in different dimensions, normal dimensions, abnormal dimensions. For example, a child with dyslexia would have a perfectly normal (or even superior) performance dimension, whereas his verbal dimension would be two standard deviations lower than the performance dimension. On the other hand, the social and verbal dimension would necessarily be worse in a person with autism, and a person with attention-deficit and hyperactivity disorder would have an attention dimension two standard deviations lower than his average ability in all other dimensions.

With such a classification, we can identify patients whose deficit is in a single dimension which may be readily treatable, and with a central registry, this can enable researchers to recruit subjects with a particular deficit to search for a treatment plan which is best suited to the children in question.

To add to the benefit, the scheme would also allow children whose disability is generalized, in which specific treatment or specific diagnosis is not helpful. 

What do you think?

[1] I am sure as hell researchers are more interested in "lesion patients" than a completely debilitated person - just look at the "Broca" patient, the "Wernicke" patient, and so on in the neurology ward, and the stroke patient beside them. You'll see the difference. The lesion patient got interviewed by 100+ medical students and junior doctors whereas the stroke patient struggle to even get somebody speaking to her.

Sunday, March 30, 2014


So, what is the requirement of water at home?

I come from pathology background -- naturally, I would look at water from a laboratory perspective. What is required for laboratory reagent water? In a laboratory, we are looking at several aspects:

(1) Ionic impurities (e.g. >10 megaohm/cm3)
(2) Organic impurities (e.g. <500 ppb)
(3) Microbiological impurities (e.g. <10 cfu/ml), and
(4) Particulate content (e.g. passing through a 0.22 um absolute screen filter)

The first one is almost an absolute requirement, that laboratory reagent water contain as little undesired ionic contamination as possible, as it will interfere with trace analysis (or if the contamination is severe, non-trace analysis -- that would be gross). The impedence of water is used as a way of measuring ionic contamination. Water has a theoretical maximum impedence of 18.2 megaohms -- and when exposed to air, the highest impedence would drop to around 1 megaohm. Water is purified to remove ionic contaminants mostly by the use of ion-exchange resins. To improve the efficiency, often multiple resins are used in cascade. 

The second one refers to the amount of organic compounds dissolved in the water. Organic contaminants can be removed by oxidation by UV light, as well as absorption and adsorption by activated charcoal.

Microbiological impurities are often removed by depth filter, and chlorination of the tap water.

Particulate content are usually removed in multiple stages: firstly, depth filter consisting of fibers interwoven to trap particulates in a random manner is used; depth filter is a high-capacity, but non-absolute filter. In contrast to depth filter, a screen filter (absolute filter) is used at the end of the water purification process to obtain an absolute cutoff. However, screen filters are low capacity with regard to contaminants, and thus a depth filter in front of it would greatly increase its lifetime.

So, for human consumption, what is the role of water treatment?

Briefly, water from the water service department in Hong Kong is considered potable - i.e. harmful constituents are at a very low level when the water leaves WSD. What is the caveat? It's the route between WSD and your home. What could go wrong?

Plastic pipe can leak organics. Old pipes (if any) could leak heavy metal ions. Bacteria can grow in the water reservoir on the top of the building. Iron oxide fragments can go into the water, etc. Another problem is the presence of chlorine in the water, which cause a change of taste.

To be honest though, none of this is significant to the extent that it is harmful to drink from the tap. And to make it clear, boiling probably does not help (other than perhaps evaporating some volatile organics). And thus, water treatment system at home is probably helpful - Take a chance, make a cup of tea with tap water, and a cup with distilled water from a reputable manufacturer - it WILL taste different. Why? - The organics, the chlorine content, hardness -- all make differences to the taste.

Thus, in my opinion, water treatment at home is mostly aesthetic (taste-enhancement) and psychological (feeling a little bit safer with regard to heavy metal which is essentially non-existent in HK).

For my home, I consider a depth filter, followed by ion exchange resins (to remove cationic [heavy metal] impurities), and activated charcoal filter to be adequate for health. In fact, for well-maintained housing establishments, this shouldn't even be necessary - except charcoal filter perhaps. Charcoal filter enhances the taste of water a lot.

There is probably little need to use elaborate deionization, osmosis or so on for home water.

Monday, March 17, 2014

Two types of oil misunderstood: Canola and coconut

Oil Facts:
1. Canola oil is not considered harmful from a toxicological aspect. In fact it's quite healthy!
2. Coconut oil, on the other hand, is not so good for your health.

Information for those who want to read a little bit more:

Canola oil
- Produced from a cultivar of "rapeseed" which is with low erucic acid content (The mustard plant)
- Erucic acid, for those who are unfamiliar with it, is a naturally-occuring omega-9 fatty acid, with a chain length of 22 (denoted as C22:1 omega-9), has not been reported to be associated with human toxicity. It appears to be toxic to mice[1].
- Current cultivars of rapeseed contain only trace quantity of erucic acid (less than 0.1%).
- Other purported toxins in rapeseed includes glucoinolates, which are said to be goitrogens (resulting in a goitre, toxic to the thyroid gland). These are at very low levels in modern rapeseed plants, which contain less than 10 umol/g, compared with broccoli, a common plant containing glucoinolates in the order of 10 mmol/g (dry weight), a 1000x difference. If you can eat broccoli, glucoinolates in canola oil is probably OK.
- It is low in saturated fat, and contain a favorable profile of omega-6 and omega-3 fatty acids.
- It has a fairly high smoke point (204 C), which is about 10 degree higher than cooking (non-extra virgin) olive oil.

Coconut oil
- It contain 91% saturated fat, the highest of all natural oils (excluding those that are hydrogenated). Taking saturated fats *cannot* be very good for your health.
- It does contain a blend of medium chain fatty acids, some of which are good (and some of which are bad) for the heart. One should also note that the famous "heart-killer" BUTTER also contain some 10% of myristic acid, which are said to be a health-promoting component of coconut oil.
- Yes, it's probably healthier than butter, but probably less healthy than even the evil canola oil mentioned above.

Some general facts of oil-making
- Other than cold-pressed oil, most oil produced nowadays include a step of solvent extraction using organic solvents such as hexane, absolute alcohol, and so on. Hexane contamination in oil is usually insignificant. Hexane is probably the least of your worries in your daily diet if you asked me. The air you breath is probably more harmful than the hexane in oil if you live in Hong Kong, given the recent pm2.5 readings.

[1] Chocolate is toxic to dogs. There are a lot of stuff that are toxic to one species and not to other. If you look into your mice biology textbook, you will get to know that they do not digest vegetable fat as well as a lot of other animals.

Sunday, March 16, 2014

A cancer diagnosed at a late stage

A recent post[1] in "名校 Secrets" surrounds a case of Stage III nasopharyngeal cancer occurring in a middle-aged lady. Following an admittedly flamebait reply, there was a lot of discussion regarding to the role of doctor in the diagnosis of early cancers.

When faced with a diagnosis of "late stage cancer", people would always look back, and try to find a circumstance when he or she mentioned her first symptom to a doctor, and try to blame them for not doing their job -- what they don't realize is that, signs and symptoms of early-stage cancers, with few exceptions, are non-specific, non-sensitive, mimics a thousand other diseases, and in general, not showing up as a "red flag" in most's eyes. And for the matter, most early-stage cancers are NOT symptomatic.

If cancers were so easy to diagnose at a early stage, we wouldn't have a problem of cancer, we won't need thousands of researchers worldwide to combat cancer, and we most certainly do not need a billion-dollar pharmaceutical industry.


Friday, March 14, 2014

Surgical mask, N95 mask...

A response to the following article:

With the current evidence, surgical mask is non-inferior to N95 respirators in preventing influenza infection, the basic reason for its existence in modern healthcare -- preventing droplet-transmitted infections[1]. It should be noted that there are multiple reason behind wearing surgical masks, such as preventing the wearer's droplets from contaminating the operating field, or decreasing the amount of droplets emitted during e.g. sneezing.
On the other hand, while there are a lot of Taiwanese and Japanese people wearing cloth mask. While there are not a lot studies on this matter, Rengasamy et al provided some evidence that it doesn't really work[2]. It's not good enough trapping anything from influenza to tuberculosis.

While we all know that we can buy N95 masks and simple surgical mask, the need for fit-testing for the use of N95 masks are often forgotten: one need to have a tight-fitting N95 masks to enjoy the benefit of a respirator: how is it different from a mask? A major difference lies in that a surgical mask filters aims at filtering only a portion of air taken by the person whereas a respirator aims at filtering all, i.e. practically all gas that you inspire went through the N95 if you are wearing it correctly.

Let me repeat it: you need to do a fit-testing to determine which N95 model fits you the best. If an N95 is not fitting, you are not enjoying any of its benefits. A simple rule is, if it feels easy wearing it, either you are working in the industry, or you are wearing it wrong.

There are some studies suggesting that N95 fit-test is not necessary[3]. However, this has not been published in a peer-reviewed journal, thus, without further studies, it is probably wise to continue doing fit-tests. A rule of thumb for those who may not have access to fit-testing is, 1860 for gentlemen, and 1860s for ladies. Your mileage may vary.

[1] JAMA. 2009 Nov 4;302(17):1865-71
[2] Ann Occup Hyg. 2010 Oct;54(7):789-98.
[3] ICAAC 2009; Oral session K-1918b

Thursday, March 13, 2014

Hard disk...


I'm about to purchase a SATA hard drive. I was wondering if, aside from the storage capacity, are there any other factors I should keep in mind? I care above all about reliability. Is a more expensive drive less error-prone than a low-end one?


Consider reading Pinheiro et al (2007) Failure Trends in a Large Disk Drive Population. Proceedings of the 5th USENIX Conference on File and Storage Technologies, Feb 2007. Just search the title on google.

In general, drives of the same manufacturer are made to the same specification in terms of the disk assembly. It is usually the tolerances that differ. To give an example, if you want a paper circle of 5cm diameter, a circle of 4.5 or 5.5 cm maybe acceptable for one use (e.g. home use for decoration of child's room) but a circle of 5.0cm, add or subtract 1mm, (i.e. within 4.9 - 5.1 cm) would be required if it is a decoration project for a project launch for some big, big company.

For example, the load/unload cycle specification of a home drive may be ~ 300,000 times, the load/unload specification of an enterprise drive would be ~ 600,000 times, doubling the figures. The tighter specification also applies to the drive assembly and the disk manufacturing process - and thus the non-recoverable read error rate would be much smaller for enterprise drives, for example, a typical, current home drive - Caviar Black (from Western Digital) would have a nonrecoverable read error per 10^14 bit read. Compare with a typical harddrive manufactured towards datacenter servers WD RE SAS, which would have a nonrecoverable read error per 10^15 bit read. Whether that 10 times more reliability matters to you, is another matter.

To be honest, how you use the drive, is likely more important than which drive you use. Below is a summary of google's findings:
  • 6-7% of the drives fail within first year of use. Within which, more than half of these failing drive will fail within 6 month. These drives tends to be utilized highly during these periods.
  • Failure of the drive follow a double peak model. The first peak is within 3 months, and the second peak is around 3 years.
  • After the first year, there is in general a 8% failure rate of harddrive annually.
  • The effect of temperature is twofold: [1] The lowest failure rate is seen at disks run around 40 degree C. [2] As the drive ages, the failure rate rises expoentially with temperature at third year. To interpret this statement, running the drive at ~35C would achieve the best compromise of longevity and early failures, and if your harddrive can be replaced every 2 years, running the drives as hot as 45C in general would in fact decrease the failure rate, but past the second year there will be an exponential increase if you run it at 45C.
  • If you use SMART reporting software (a nice one is Crystal Disk Info URL: ), if you see one scan error, 10% will fail within days, and 30% of the drive will fail within 6 months. Thus, backup and discard the drive accordingly after you see the first one. If you see a reallocation event, 10% will fail within ~4 months. Note, however that only 60% of all harddrive failures would be predicted by SMART system.

Mean time between failures is basically not very useful for the typical consumers. The Mean time between failure is usually ideal and theoretical. Let's say we have 500,000 drives with MTBF of 500,000 hours - if you run each and every of them together you will likely to have one of them failing every hour, statistically speaking, if you run them within their specification (temperature, humidity, power supply quality...) With reference to the google study, the realistic useful life of a harddrive would be more like 2 years (in a non-redundant system) or 3 years (in a redundant system) - if you use it 24 hours a day - In a redundant system (e.g. a RAID-[5,6]) you can lose a harddrive without losing data. Particularly, in RAID 6 you can lose a harddrive and still have redundancy during the rebuild process.

Service life

One often see some manufacturer quoting service life such as '5 years' and then offering you a warranty of '3 years'. Translation: "We believe that it should last some 5 years. If it fails within the first three years of use, we'll replace it at our cost, but if you have it failed between 3rd and 5th year, poor you. It certainly won't be the case that we have installed some sort of time bomb to make them unusable by its fifth birthday, but you should get a new harddisk and use instead of this 5-year-old harddrive if your data is any precious."

Saturday, March 8, 2014

Allocation of resources: you can't put all bucks in one bucket.

"Selfishness is the greatest curse of the human race." -- William E. Gladstone, four-time prime minister of the U.K. 
With the great increase in the life expectancy in our population, and the advances in medical technology, we are seeing more and more people becoming chronically debilitated, rather than dying from the outset; and with the advances in pharmaceutical industry, we are more able than ever in prolonging life, as well as improving quality of life in patients who would have otherwise died or suffer an ailment that would be worse than dying.

These wonder drugs, however, do not come without a steep price. The question then, is how much is the society willing to pay for these patients? If there is a cap as to how much we're going to pay, would it be based on a "per capita" basis, "per diagnosis" basis, or "per quality-adjusted life-year gained" basis? What is the price of a quality-adjusted life-year?

Taking the most extreme example, given a dose of loratadine (less than $1 hkd/day), and I can be free of my allergic rhinitis symptoms. This facilitates my performance at work, and I guess perhaps I can proudly say that taxpayers funding me the treatment (in the form of a prescription under HA) is probably fair.

On the other hand, a patient with terminal cancer may have his or her life extended by three months by the use of multiple targeted therapy, which can cost more than $10,000 a month per drug. Is that good use of taxpayer money? I shall leave that to the readers to judge. The question for those who answered "yes" is that, what is the opportunity cost for others in giving this patient his/her much-needed targeted therapy drugs?

I think the current approach of using a drug formulary to limit the spending is probably wise. On a side note, none of the psychiatric drugs used currently are "self-financed items". Many are under "special drug" label, but no, patients do not need to pay using these drugs.

Postscriptum. this is a response to "在香港做人,還是仆街到底比較好", Accessed 8 March 2014, URL:

Psychiatric disorder: Bipolar disorder

I guess a blog named pathological mind would not be complete without a touch on psychiatric disorders, and thus, perhaps the topic for today would be bipolar disorder. I decided not to cover treatment though, for I, admittedly, are not so updated with respect to the advances of treatment in the area.

MDD: Major depressive disorder (i.e. depression)

Bipolar disorder (or manic-depressive illness) is often a severe, chronic illness chracterised by periods of depression and elation. Manic and depressed phase are both associated with significant morbidity and mortality. Bipolar disorder is usually divided into two forms, I and II. The diagnosis of bipolar I disorder requires a manic episode.

A manic episode is characterized by seven features, which I remember by the mnemonic "fidgets" -
  1. Flight of ideas (the subject feeling that thoughts are going too fast),
  2. Increased goal-related activity, 
  3. Distractibility, 
  4. Grandiosity (thinking that one is of a great status, etc.)
  5. Excessive pleasurable activity, 
  6. Talkative, 
  7. Sleep disturbance

The individual may also have experienced depressive episode or mixed episodes of manic and depressive symptoms in the past.

The diagnosis of a bipolar II disorder requires at least 2 prior major depressive episode and a hypomanic episode. Once an individual is diagnosed of a bipolar I or bipolar II disorder, the diagnosis during subsequent mood episodes continues to be bipolar disorder, with the most recent episode being described as depressed, hypomanic or manic.

Clinical features

Patients with bipolar disorders common experience several major depressive episode prior to their first manic or hypomanic episode. Early in the illness episodes of depression or mania are separated by relatively long periods of normal behavior, but without treatment subsequent episodes become increasingly frequent.

Untreated manic or depressive episodes typically last several months. Treatment results in shortening in length and decrease in severity.

Rapid cycling form of bipolar disorder affects 10-15% of the patients and is characterized by increased frequency of episodes to 2-4 times per year. This form is associated with a poor prognosis and is less responsive to treatment.

Psychotic symptoms may develop during any manic episode, but once present subsequent manic episodes are more likely to be accompanied by psychotic features. Approximately 20-30% of patients with bipolar disorder, and 15-20% of patients with bipolar II disorder (patients who experience hypomanic episodes with depressive episodes) do not experience total recovery between episodes.

Prevalence and heritability

The prevalence of bipolar disorderis about 1.5% and 3% of the general populaton. The lifetime prevalence is approximately 0.8% for bipolar I disorder, 0.5% for bipolar II disorder. The prevalence of these disorders are the same for male and female. 

Bipolar disorders cluster in families. For bipolar I disorder, the risk among first degree relative is 6-7% for bipolar I disorder, 2-5% for bipolar II disorder and 25-35% for MDD. Concordance rate for the monozygotic twins is 75% for bipolar disorder and 50% for major depressive disorder, suggestive of nonheritable as well as heritable factors in disease expression.

In contrast, first degree relatives of patients suffering from bipolar II disorder is at significantly increased risk of developing bipolar II disorder and MDD but not bipolar I disorder.

Twin, adoption and family studies indicate that genetic factors substantially contribute to the liability for developing bipolar disorder and major depressive disorder. The earlier age of onset appears to be associated with increased transmissibility of both bipolar disorder and MDD.

Taken at face value, adult twin and adoption studies indicate that familial transmission of bipolar disorder is largely a result of genetic factors and that genetic factors are more important in the development of bipolar disorder than in depressive disorder.

The heritability of bipolar disorder is estimated to be 60-70% whereas that of adult MDD is about 40%.


Bipolar disorder, like MDD, carries an increased risk of suicide and accidental death. Suicide are more common during depressed or mixed manic/depressive episodes, and while intoxicated.

Accidental injury or death are more common in manic state because of poor judgement and increased risk-taking behavior. In the elderly, mania is associated with increased medical morbidity due to malnutrition and exhaustion states from increased activity and decreased sleep.

Mania, hypomania and cyclothymia are all associated with occupational, scholastic and social impairment. The risks of comorbidities such as alcoholic abuse are markedly increased.

Patients with mixed manic/depressive episode appear to have the highest psychosocial morbidity.

Patient behavior - sense of entitlement

Whereas doctors working in the private sector generally enjoyed great respect from their patients -- as a professional whom their patient consults, doctors working in the public sector generally do not
enjoy such status. The trouble? Wages are being paid by the taxpayers, and this often create a sense of entitlement among the citizens.

Given the amount of work, it is not surprising that most doctors staying in the public sectors are enthusiastic towards patient care and are eager to help their patients. However, it should be borne in mind that we doctors are also human beings and have our families and life outside work.

Consider these three questions:
  1. If you are rude, can you expect the doctors to stay professional in their judgement?
  2. If you are swearing, can you expect others to be caring for you?
  3. If you are attacking their colleagues, can you expect them to uphold their professional standards and give their best to treat you?

Unfortunately, for the doctor, their answers to these three question needs to be "yes". However, I wouldn't be expecting a doctor to stay smiling when faced with personal attacks.

"Disorders", "diagnostic labels", and why getting it diagnosed.

More and more people are being diagnosed to have a psychiatric disorders. The keyword here is "disorder". We shall look at how a "disorder" is defined - in essence, in most psychiatric guidelines or manuals, a condition can only be said as an disorder when it causes impaired function in social, occupational, or educational aspects of life.

And when we evaluate the requirements for social, occupational, and educational aspects of life - we can see that over the past 20 years, these requirements have been a monotonous increasing function.

It is perhaps thus to nobody's surprise that we have more such "disorders" diagnosed, especially in Hong Kong. In other countries, and in other cities, if you are not the kind to live in cities, you can move elsewhere, and work a easier life. Not so much in Hong Kong -- there's nowhere to go. Perhaps jumping from height or into the sea, but that's it. It is so unacceptable socially that a person from Hong Kong would go elsewhere to live a lowly life that people would choose to die over going elsewhere.

Definition is one thing, and then we have several groups with vested interest in giving a "diagnosis" to patients: parents, and perhaps patients. Nowadays, instead of "laziness" and "stupidity", people are increasingly referring their child as being inflicted by developmental delay (which is otherwise known as "stupidity" in my days, especially when they are not formally "mentally retarded"), attention-deficit hyperactivity disorder (which is known as "lazy and distracted"), and so on, so forth.

It has become a trend such that all child are bright and beautiful, and only afflicted by a disorder and is therefore so naughty that you teacher cannot work with them. And it's your fault by not coping well with their illness, or by discriminating them based on their ailment.

Honestly, I don't believe in the notion that this generation of children is facing a "psychiatric epidemic".  In my humble opinion, they are facing a "diagnosis epidemic".

People see doctor, people die.

IT is sad that every two or three weeks, we're seeing episodes and episodes of people suffering because the waiting time for special out-patient departments are long. Don't be mistaken - I agree that it is indeed long, what I wanted to say though, is that these high counts of mortality is probably less related to the long waiting time. I believe, however, this is due to patient behavior, as opposed to negligent doctors, failing standards, or poor medical system.

It is, again, a recurring theme that wherever there are poor outcomes, people ask for somebody to take up the responsbility, typically a scapegoat in my humble opinion. People tends to blame the establishment, such as the hospital management, the lengthy waiting time, the lack of medical manpower, or sometimes, it could even be targeting those doctors who are not willing to work too many hours overtime. However, it is very much less common that we see people blaming the patient.

When patients visit their doctor, we call it consultation, and we charge the consultation fee. What this mean is that the doctors are consulted, and to spell it out clearly, if the patients do not visit their doctors, the doctors could do nothing. I think it could be said that our patient population in general has been educated to come to the emergency department whenever their condition changes for the worse.

In this case[1], the gentlemen went to general out-patient clinics for depressed mood. Apparently, what the medical officer did was to refer him for psychiatric evaluation, which, in my books, it means that this patient does not have severe psychiatric disturbances, and there were no signs or symptoms that are suggestive of him being at risk of harming himself or others. Subsequently, he has been evaluated (probably by psychiatric advanced practice nurses -- who are extremely familiar with psychiatric conditions) and was given an appointment ten-eleven months down the road.

What he did was that he killed himself three days after receiving the appointment. At this point it is important to stress on that we doctors works with uncertainty, and are definitely not fortune-tellers who can see the future through a ball of crystal. And for the matter, if any medical graduate could see the future, it's probably better to win a mark-six ticket every now and then instead of working 60+ hours in the hospital every week. 

What is the lesson learnt? If you have got a patient at home, and you see his or her condition changing for the worse, bring them to the emergency department -- this, is the raison d'etre of emergency department.