For one elderly patient, a thin acupuncture needle inserted the back caused a world of hurt when two days later she ended up in hospital with a collapsed lung. But even though this situation was rare, it's not exactly an unprecedented event.

Acupuncture isn't risk free, and practitioners of the treatment might not always be familiar with the anatomy they're working with. This is evident in the current case of a 79-year-old woman from Portugal, recently reported by doctors from the Centro Hospitalar Universitário de Lisboa Central.

The elderly woman first showed up at the clinic with moderate breathing difficulties. An X-ray quickly revealed the cause – the bottom of her right lung had been indented in by a distance of 2.3 centimetres (about an inch), in a condition known as pneumothorax, what we commonly call a "collapsed lung".

Lungs don't tend to simply collapse in on their own. For this to happen, air needs to enter the pleural cavity - the space between the lung and the chest wall.

Sometimes this air can leak out from a damaged or diseased lung. In this case, the cause was found to be a thin whisper of a needle that had been briefly inserted into the patient's back two days prior, in an attempt to treat chronic back pain.

Acupuncture is commonly promoted as an ancient Chinese medical treatment capable of easing a range of discomforts, treating illnesses, or promoting health and fertility.

While it can involve a range of methods – including modern touches such as the application of electricity, ultrasound, lasers, or even bee stings – most still centre on the insertion of metallic needles into the skin at key points in the body.

The exact age and origins of the practice is disputable, just as most specified benefits have been found wanting under scientific scrutiny. When it comes to many specific claims, such as improving chances of conceiving in IVF, poking the skin with needles doesn't seem to help.

As for the treatment of pain and other personal discomforts, the evidence isn't overwhelming, hovering somewhere between 'might be something to it in some cases' and 'if we have to look this hard, is it really all that useful?'.

Not that questionable scientific evidence has impacted the popularity of these needles. Along with other forms of traditional Chinese medicine, acupuncture is rapidly becoming a mainstream form of healthcare around the globe.

Part of the practice's appeal is that it seems like a low risk, safe alternative to taking medications or other forms of medical intervention.

While true for the most part, complications can and do arise. Most are relatively minor complaints, such as bleeding and localised pain. But more serious complaints aren't unknown.

Although a German review of nearly 230,000 acupuncture patients back in 2009 found only two examples of pneumothorax, a WHO review of Chinese scientific papers has found 201 cases of it reported in the literature in the last 30 years.

In this case, the needle had been inserted into a space near the patient's shoulder blade where the lung can come within centimetres (less than an inch) of the surface of the skin. Get the angle and depth wrong, and a needle can literally pop the pleural cavity.

The woman's treatment required the extremely painful insertion of a chest tube with local anaesthesia, as well as several days of observation while on oxygen and painkillers.

The good news is she survived the ordeal. As it was also her first acupuncture experience, we wouldn't be surprised if she doesn't go back to the needles.

Even when it's something so rare as this event, patients have the right to determine if slim risks are worth the gamble. This poor patient didn't know pneumothorax was a possible side effect, and there's a chance her acupuncturist didn't, either.

Providers of any kind of medical treatment – whether it's evidence based or alternative – have a responsibility to not only be informed themselves, but to make their patients aware as well.

"Acupuncturists must know the anatomical structures and layers that are located beneath all the acupuncture points, especially for high-risk acupuncture points," the doctors advise in their case study.

We'd all like alternatives to risky healthcare. Unfortunately, the best we can ever do is use science to know what the chances of complications are and ask if we're prepared for the worst.

This case study was published in BMJ Case Reports.