The death of a schoolboy with a dairy allergy after cheese was thrown at him could be the first known case of its kind, an expert has said.

Karanbir Singh Cheema, 13, known as Karan, went from “absolutely fine” to unconscious in less than 10 minutes after the incident at William Perkin Church of England high school in Greenford, west London, on 28 June 2017.

Dr Adam Fox, a consultant paediatrician brought in by the Metropolitan police to review the case, told an inquest at St Pancras coroner’s court into Karan’s death on Friday that anaphylactic shock brought about by skin contact was “extraordinarily unusual” and he had never heard of it resulting in death.

“Severe allergic reactions through skin contact are very uncommon … if it was skin contact alone that caused, in this case, fatal anaphylaxis, I believe that would be unprecedented … I have never seen it before. I have been unable to see any cases reported of a fatal anaphylaxis [through skin contact],” he said.

Fox said he had consulted both global and domestic literature and found previous examples of contact with an allergen through the skin resulting in “bronchospasms” (caused by construction of the airways), but not fatalities.

The consultant said the rarity of the event suggested there could be other factors at play; Karan also had asthma and chronic eczema.

But Fox said the fact that Karan was scratching his neck after the cheese was thrown at him by a fellow pupil suggested that he did go into anaphylactic shock as a consequence of the contact with the food, as that was known to be the point of impact.

Fox added that Karan’s scratching, which other witnesses have said was so frenzied it drew blood, could have inadvertently exacerbated the situation. “Further scratching and degrading of the skin barrier could well have led to further contact [with the allergen],” he told the inquest.

He said the high pollen count on the day in question could also have had an adverse effect on Karan and that being Asian, a boy and a teenager increased the probability of him experiencing a severe allergic reaction.

Fox also suggested that the EpiPen given to Karan could have been administered sooner, although he said it was not intended as a criticism of the school staff who tried to help him. “If someone tells you they need their inhaler, then that’s a very clear sign you need to get on with the EpiPen,” he said.

Earlier, the senior coroner for inner north London, Mary Hassell, described the response of Alexandra Ulrich, a senior paramedic, as “a little bit panicked”.

She made the observation after Ulrich told the court she did not establish that Karan had suffered an allergic reaction until she was unloading him from the ambulance at the hospital.

Ulrich, who has worked at the London ambulance service for more than 10 years, said she would have done things differently had she known earlier about the contact with an allergen.

However, Dr Andrew Jones, a paediatric consultant at Great Ormond Street hospital, where Karan died 10 days later, said he did not believe the schoolboy’s prospects for survival were diminished as a result.

He said Karan died after his parents agreed to gradually withdraw the drugs that were keeping him alive. He said the cause of death was severe global hypoxic brain injury and anaphylaxis.

The boy who flicked the cheese and another pupil who passed it to him, both aged 13 at the time, told the inquest on Wednesday they were unaware Karan had an allergy to the food.

However, Dame Alice Hudson, executive headteacher of the Twyford Trust, encompassing William Perkin school, told the inquest: “It’s my view that there was a very good general awareness of his allergies in relation to both bread and cheese.

“From my experience in interviewing the students, I would say they did have that awareness and were being very careful about what they said. It may be them trying to support themselves from something that would be very painful to admit.”

However, when questioned by the coroner, she added: “There’s a possibility that their reaction was due to general fear rather than a specific knowledge [of Karan’s allergy].”

Within 10 minutes of the incident, Karan – described as “so bright he could have been anything he wanted” – was unconscious.

After closing statements were made, the coroner said she would hand down her conclusions next Friday at 1pm.

Hassell said she would be issuing more than one prevention-of-future-deaths report and that it was “doubly sad” that she had previously made recommendations relating to a death in similar circumstances.