The Richardsons (whose real name has been withheld for patient confidentiality reasons) had been awaiting their beach holiday in Thailand for weeks. With powder-white beaches and azure seas, the family of three looked forward to a week of fun and relaxation with friends. But days before their scheduled departure from Hong Kong, eight-year-old Ben came down with flu-like symptoms. With a 39-degree Celsius fever, cough, runny nose, body aches and fatigue, he was in no condition to travel. The Richardsons told their friends they would meet them at the resort after Ben's symptoms cleared up in a few days. Their friends, including Dr Julie Chen, an assistant professor with the department of family medicine and primary care at the University of Hong Kong, went ahead to Thailand. Ben's symptoms faded after a few days, and the family caught the first flight there. After arriving, however, the boy's parents noticed a mild fever had returned. Ben also complained that his calves ached. Thinking that it was probably the strain of travelling so soon after a flu, Ben's parents figured he just needed a quiet evening and a good night's rest. But when Ben woke up the next morning, he couldn't get out of bed because it hurt to walk. To go to the bathroom, Ben crawled to avoid putting any weight on his legs. In their consternation at their son's physical complaints and behaviour, the Richardsons called Chen for help. Although Chen was not currently in medical practice, she had been trained as a family doctor in Canada. When the Richardsons first described Ben's symptoms, Chen had a flash of concern that Ben might have rhabdomyolysis, a condition in which the muscle fibres break down, generating muscle weakness and pain. Another possibility was Guillain-Barre syndrome, a post-flu complication in which the immune system mistakenly attacks the nervous system, resulting in muscle weakness that ascends from the legs to the upper body, eventually leading to paralysis. In these situations, she realised that Ben would need immediate hospitalisation, but the nearest hospital was three hours away. She hurried to the Richardsons' room. She was greeted enthusiastically by Ben, who was sitting up in bed and playing computer games with great gusto. She examined him and found he was perfectly healthy with no fever, rash or swelling or other unusual signs, except for tenderness in his calves when touched. More importantly, he reported that his urine was pale yellow, thereby reducing the likelihood of rhabdomylysis, which often is accompanied by dark red or cocoa-coloured urine. He also had no other symptoms that might hint at Guillain-Barre syndrome. With mischievous delight, Ben showed Chen that he had found a new way of moving around with minimal pain to his calves - he curled his toes under his feet and walked on his toe 'knuckles'. Ben suffered acute calf pain only when he tried to stand or walk normally. Ben's sprightly behaviour and unusual condition was baffling. Although concerned about the calf pain, his parents took comfort in his otherwise normal, peppy behaviour. Hence, they were reluctant to make the three-hour trip to the hospital. In the hopes of finding out more about the cause of Ben's pain, Chen searched the internet for conditions with his symptoms. To her surprise, several case studies showed up that were close matches. They described a rare condition called Benign Acute Childhood Myositis (BACM). With BACM, which tends to affect male school-age children, an upper respiratory tract infection with flu-like symptoms are followed by a sudden onset of calf pain and an inability to walk. While its causes are unknown, it appears more often associated with the influenza B strain. Despite its dramatic presentation, BACM is not serious and will suddenly vanish. Chen shared this information with Ben's parents. In light of Ben's classic presentation and otherwise good health, his parents decided to keep him under close observation, with the expectation that the BACM would disappear quickly. Ben borrowed a wheelchair from the hotel and showed no signs of worsening physical distress. About 36 hours after the calf pain began, Ben astonished everyone by suddenly jumping up and running off to play. The BACM had run its course. Looking back, Chen says that had medical assistance been more easily accessible, she would have sent Ben for tests to rule out other causes. At it was, the Richardsons had a memorable holiday story to tell.