Cases/Smoking, Alcohol and Substance Misuse

Tingling Feet Who Uses Nitrous Oxide At Parties — Free SCA Practice Case

Student with tingling feet who uses nitrous oxide at parties

Station Timer

12:00

Golden Minute

Initial Introduction

•Introduce yourself

•Ask an open question — "How can I help you today?"

•Listen — don't interrupt

•Catch early cues

Data Gathering

History, ICE & Diagnosis

Clinical Management

Diagnosis, Plan & Decisions

Safety Net

Follow-up & Close

12:00

Golden Minute

Try 5 free cases

Five cases are free: a live 12-minute consultation with an AI patient each, marked, and no card.

Materials for Candidate

Please review before starting the consultation

Patient Profile

Full Name

Caleb Fashola

Age

19 years

Consultation Type

Video

Age

Situation

Video Consultation. Appointment booked by the patient for today.

Reason for Encounter

"Numb, tingling feet for two weeks."

Medical Records

●PMH: Mild childhood eczema, no treatment for years. No previous neurological symptoms.
●Medications: None.
●Allergies: NKDA.
●Social: Second year university student, new to the practice 18 months ago. Lives in a shared house.

Recent Notes

●Registration health check, 18 months ago: BMI 22. No concerns recorded.

Patient Script

For the friend playing the patient role

Character Overview: You are Caleb Fashola, a 19 year old second year geography student. You share a rented house with three course mates, including your closest friend Hugo. Your mother, Folake, is a nurse in another city and rings most Sundays, and your sister Dara is at school. You have been vegetarian since you were 14, mostly living on pasta, chips, cereal and veggie burgers. You are easygoing and chatty, and you joke when you are nervous. For two weeks your feet have felt numb and tingly, as if they were asleep. You have been bumping into things in the dark and feel wobbly. You put it down to a new pair of flat trainers you bought a month ago, and you have booked in for something to help the feet. You do not connect it with the gas you inhale at weekends and you do not mention it unless asked directly about drugs, alcohol or anything you take for fun. Your voice is light and quick at first, and goes quieter when you are asked about the gas.

Opening Sentence: "Hi, doctor. This is a bit random, but my feet have been numb and tingly for about two weeks. I think it's my new trainers, they're flat and hard. Could I get a cream or something for it?"

History if Asked (Data Gathering Phase)

●How it started: "About two weeks ago I noticed my toes felt fizzy, like pins and needles that didn't go away. I thought it was the trainers because I'd just started wearing them every day. Over the last week it's crept up the foot, and it's both feet."
●Where it is: "Both feet, the soles and the toes, and a bit up to my ankles. It's the same on each side. Nothing in my legs above the ankles."
●What it feels like: "Numb, like walking on cotton wool, with a buzzing, tingly feeling. It's not painful. It's worse in the evenings."
●Hands: "Now you say it, the ends of my fingers have been a bit buzzy this last week. I thought it was typing."
●Balance and walking: "I'm wobbly, especially in the dark. I've walked into the end of my bed at night twice. In the shower, when I shut my eyes to rinse shampoo, I have to put a hand on the wall or I feel like I'll tip. In daylight I'm mostly fine."
●Strength: "My legs feel a bit heavy and tired going upstairs. I haven't actually fallen. My grip is okay."
●Back and neck: "No pain. But a few times, when I look down at my phone, I get a quick electric zap down my back. It's over in a second."
●Tiredness: "A bit more tired than usual, and a bit out of breath on the walk to uni. I put that down to late nights."
●What he has tried: "Different socks, and going barefoot at home. Nothing makes any difference."

Ideas, Concerns, Expectations

Gating note: Caleb does not raise any of the following himself. Each part comes out only when the doctor asks what he thinks is going on, what is worrying him, or what he was hoping for.

●Ideas: He is sure it is the new trainers squashing the nerves in his feet. He is a little thrown that it is in both feet and now his fingers. "It's the trainers, isn't it? They've got no cushioning. But it's weird that it's my hands as well."
●Concerns: He is quietly worried that it is something serious that could stop him walking, and he has been trying not to think about it. He also worries that his mother, who is a nurse, would find out and make a fuss, and that admitting to the gas will get him into trouble. "I don't want to end up unable to walk. And if my mum finds out she'll go mad."
●Expectations: He expects a cream or a vitamin and to be sent home with advice on better shoes. He would like this over quickly. "I thought you'd say get some better shoes and maybe give me a cream. I didn't think it'd be a big deal."

If Asked: Medical History and Medications

Gating note: Caleb answers each of these plainly when the doctor asks about it.

●Other health problems: "Nothing. I had eczema as a kid. No operations, no hospital stays, nothing like that."
●Medicines and supplements: "None."
●Diet: "Vegetarian since I was fourteen. I eat eggs and cheese now and then. No vitamins and I've never had a blood test."
●Mood and sleep: "Mood's fine. I'm sleeping okay. A bit stressed about coursework, but nothing worse than my housemates."

Social History and Lifestyle Impact

●Home and study: Lives with three course mates in a rented house, ten minutes by bus from the practice. He walks to lectures and is getting through the day, but has skipped his Wednesday lab session, which he does not want his tutor to notice.
●Alcohol: "A few pints at the weekend, ten or twelve over the week at most."
●Smoking and vaping: Vapes occasionally at parties. No cigarettes. Cannabis once or twice a month, nothing else.
●Recreational gas: Gating note: only when the doctor asks about drugs, recreational substances, party habits or anything he takes for fun. At first he downplays it. "Oh, just laughing gas. Hugo gets the big cylinders delivered. It's not really a drug, is it? It's what they use at the dentist." If asked how much: "Most weekends, I'd say about two or three of the big cylinders between four of us over Friday and Saturday, and I'd have a good share of that. It crept up over the last six months. This last month there have been some Thursday nights too, because someone always has a cylinder lying around." He fills balloons from the cylinder. He has been dizzy and giggly but has never passed out. If the doctor links it to his feet: "It's just balloons, though. Surely that can't be it?"
●Legal position: If asked, he has heard it was banned but says "everyone still does it and nobody gets stopped."
●Other drugs: No ketamine, MDMA, cocaine or injecting.
●Friends and housemates: Hugo and the others use it too, and it would be awkward to be the one who stops. Nobody else has noticed any problems.
●Availability to be seen: He can get to the surgery in about an hour. He has no commitments after midday.

If Asked: Associated Symptoms

Gating note: Caleb answers these only when asked. Every one is negative unless stated.

●If asked about bladder or bowel: "No change. I'm going to the toilet normally and no accidents."
●If asked about numbness around the bottom or genitals, or sexual function: "No, nothing there and no problems."
●If asked about weakness in his arms, a dragging foot, falls or his speech: "No, not weak as such, just heavy on the stairs. No falls and my speech is fine."
●If asked about vision, headaches, fever, rash, recent illness or weight loss: "No to all of those."
●If asked about memory or concentration: "My concentration has been a bit rubbish, but that's the late nights."
●If asked about a bad taste, sore tongue or mouth ulcers: "My tongue's been a bit sore at times. Nothing else."
●If asked about stomach or bowel conditions, anaemia or thyroid problems: "No."

Responses to Management (The Negotiation Phase)

●
If the doctor links the symptoms to the gas and explains that it can damage the nerves:
- ●Reaction: Shocked and defensive. "But it's just gas. It's what they use at the dentist. How can that damage nerves?" He listens if the explanation is clear and plain, then goes quiet. "Is it permanent? Am I going to end up in a wheelchair?" If told that most people improve if treated early, but some are left with lasting symptoms, he asks: "How long will it take to get better? Will I be able to walk normally?"
●
If the doctor says he needs to be examined and probably tested today, or at hospital:
- ●Reaction: Resistant at first. "Today? Can't it wait until Monday? I'll stop this weekend, I promise." He accepts when told that nerve damage can progress and that treatment works best the earlier it starts. He asks what will happen when he gets there. If asked to test his own balance or reflexes on screen, he declines and asks to be checked in person.
●
If the doctor suggests blood tests and vitamin B12 injections:
- ●Reaction: Curious and a bit confused. "What's vitamin B12 got to do with gas? I eat okay." Once told that the gas stops the body using B12, even if the level looks normal, he accepts it. He asks how many injections he will need and whether tablets would do. If told injections are used first because of the nerve symptoms, or that the specialist may advise tablets, he agrees.
●
If the doctor advises him to stop or cut down:
- ●Reaction: Honest and a bit stuck. "Do I have to stop completely? What if I cut down to a couple of balloons? Hugo and the others will take the mick." He asks "If I take B12 tablets, can I carry on?" If offered local support or advice, he accepts a leaflet or a link, and asks "Will it be on my record?" and "Do I need to tell the uni?"
●
If the doctor discusses confidentiality, the police or his mother:
- ●Reaction: Anxious until reassured. "Are you going to tell the police? Or my mum?" He relaxes when told that what he says stays in the surgery. "I'd rather tell her myself, if I have to." He will tell the hospital about the gas if the doctor explains why it matters.
●
If the doctor gives safety netting:
- ●Reaction: Wants specifics. If it is vague, such as "come back if it gets worse": "Worse how? What would make it an emergency?" He repeats back what to look for and where to go when given symptoms such as new weakness in the legs, trouble passing urine or opening his bowels, numbness around his bottom, falls or struggling to walk. "So if my legs give way I go to A&E, not wait for the surgery?"

Mark Scheme

Domain 1: Data Gathering and Diagnosis

0 / 16 indicators checked+0−0

Positive (0/8)

Negative (0/8)

Domain 2: Clinical Management and Medical Complexity

0 / 22 indicators checked+0−0

Positive (0/11)

Negative (0/11)

Domain 3: Relating to Others

0 / 14 indicators checked+0−0

Positive (0/7)

Negative (0/7)

Clinical Learning Points

The Core Dilemma and the Model Plan

●Caleb is a 19 year old with two weeks of numb, tingling feet, spreading to his fingertips, with unsteadiness in the dark. He blames his trainers and expects a cream. The station tests whether the candidate looks past the stated reason, asks about drugs, recognises nitrous oxide nerve damage, and acts the same day.
●The model plan has five parts. Take a focused history that includes recreational substances, diet and the neurological red flags. Recognise probable nitrous oxide related vitamin B12 dysfunction with myeloneuropathy (damage to the spinal cord and peripheral nerves). Arrange same day assessment in person with specialist input. Make sure B12 replacement starts promptly, whoever gives it. Advise him to stop completely, with harm reduction, support and specific safety netting.
●Acceptable alternatives: examining him at the surgery within hours, taking bloods, speaking to the on call neurology or medical team, and starting hydroxocobalamin in primary care if the specialist advises; or sending him directly to the acute medical unit or emergency department with a clear handover. Either way he must be seen in person the same day. Waiting for blood results, or a routine referral, is not acceptable. No UK guideline fixes this timescale; it is a clinical judgement standard, because progressive gait and sensory symptoms with heavy legs suggest possible spinal cord involvement.

How Nitrous Oxide Damages the Nervous System

●Nitrous oxide oxidises the cobalt in vitamin B12 (cobalamin) and so inactivates it. The body then cannot make methionine and myelin, the insulating layer around nerves, breaks down. The dorsal columns of the spinal cord, which carry joint position and vibration sense, are affected first, and the picture resembles subacute combined degeneration.
●Typical symptoms are tingling and numbness in the feet then the hands, a sensory ataxia (unsteadiness that is worse in the dark or with eyes closed, because the brain relies on vision for balance), heavy or weak legs, and Lhermitte's sign, an electric shock down the spine on neck flexion.
●The MHRA Drug Safety Update (2014) states that neurological toxic effects can occur without anaemia or macrocytosis, and even when B12 levels are in the normal range. NICE NG239 agrees: do not rule out B12 deficiency on the absence of anaemia or macrocytosis, and total or active B12 can look normal in nitrous oxide users because the vitamin is inactivated. A normal blood count or serum B12 therefore never excludes the diagnosis. Heavy use and a diet low in B12, such as Caleb's vegetarian diet, increase the risk.

Take the History That Finds It

●Both feet, the hands, balance in the dark and leg heaviness do not fit a shoe problem, so the trainers are the cue to widen the question.
●Ask about recreational drugs without judgement, for example: "A lot of students tell me they use things at parties. Do you use anything, including laughing gas?" Then quantify: the number of cylinders, how often, how it has changed, other drugs and alcohol. Caleb's use has risen over six months and now includes some weekdays.
●Screen for red flags of spinal cord and cauda equina involvement: bladder, bowel, saddle numbness, sexual function, weakness and falls. Caleb has none, but heavy legs and gait change show that the cord may be involved.
●Other causes of symmetrical neuropathy include alcohol, diabetes, thyroid disease, medicines and HIV. A brief screen is sensible, but nitrous oxide use and a B12 risk diet explain the picture.

Why Same Day Assessment in Person

●A neurological examination (gait, Romberg test, joint position and vibration sense, reflexes, power and plantar responses) cannot be done on video, and the patient must not be asked to test himself. The positive answer is arranging examination in person today.
●Progressive sensory and gait symptoms suggest cord involvement. Spinal imaging and treatment decisions belong to the acute medical or neurology team. This is why a same day discussion or acute assessment is expected, not a routine referral.
●Myelin damage can progress, and recovery is best when treatment starts early. Caleb will want to wait until Monday; explain why not.

Investigations and Treatment

●Bloods: NG239 (recommendation 1.3.3) says that when nitrous oxide is the suspected cause the initial test is plasma homocysteine or serum methylmalonic acid, not total or active B12. Homocysteine needs secondary care phlebotomy (the sample needs ice); MMA is more practical in primary care. Add a full blood count, B12 and folate, and consider glucose or HbA1c, renal, liver and thyroid function to exclude other causes. Take samples before B12 is given (1.3.4).
●Do not wait for results. Take the bloods first, then start treatment. Never give folic acid alone before B12 is replaced, as it can mask the problem and worsen nerve damage.
●The BNF regimen for B12 deficiency with neurological involvement is intramuscular hydroxocobalamin 1 mg on alternate days until no further improvement, then 1 mg every 2 months (a BNF indication for macrocytic anaemias with neurological involvement, applied here by extension). NG239 (1.5.8) says either intramuscular or oral replacement may be offered for nitrous oxide related deficiency, by clinical judgement and preference, and it does not address myelopathy separately. With established neurological signs, prompt intramuscular treatment is the expected route; oral replacement is acceptable if the specialist team advises it.
●NG239 also says to advise him to stop, and to review the need for replacement once he has stopped and is symptom free. Treatment works only if exposure stops. Continued use can cause relapse or permanent damage.

Advice on Stopping and Harm Reduction

●The clear advice is to stop using nitrous oxide completely. Further exposure risks permanent damage, and B12 tablets taken alongside regular use should not be presented as making it safe.
●If he is not ready to stop, or if he uses again, discuss immediate harms: fainting and falls, injury, and suffocation from lack of oxygen, which has caused deaths, especially when used alone, in a confined space or by inhaling directly from a cylinder. Mixing with alcohol or other sedatives and driving after use add to the risk.
●Support: local drug and alcohol services, the university wellbeing team, and the FRANK helpline. Peer pressure from housemates is a real barrier, so practical steps matter more than a demand to promise.

The Legal Position and Confidentiality

●Nitrous oxide became a Class C drug on 8 November 2023 under the Misuse of Drugs Act 1971 (and Schedule 5 of the Misuse of Drugs Regulations 2001). Before then possession was not an offence. Possession is now an offence where it is intended to be inhaled for its psychoactive effects, with up to 2 years in prison, an unlimited fine or both for serious repeat offenders; supply carries up to 14 years. Medical use remains lawful (GOV.UK, Nitrous oxide ban: guidance, 2023).
●The doctor's role is clinical, not enforcement. A patient who discloses use of a controlled drug is not reported to the police, and confidentiality applies in line with GMC guidance. His mother, the university and the police are not told without his agreement, unless there is a serious risk of harm. The receiving hospital team needs the history, and he should agree to it being shared.
●Telling him it is legal, or using the law as a threat, are both mistakes. State the position briefly and return to the clinical plan.

Prognosis, Safety Netting and Follow Up

●NG239 says symptoms could start to improve within 2 weeks but this may take up to 3 months, may take much longer to disappear altogether, and could worsen initially. Most people improve with B12 replacement and abstinence, over weeks to months. Some are left with persistent numbness, balance problems or weakness, particularly if treatment was delayed. Avoid promising a full recovery or predicting a wheelchair.
●Safety netting should name the symptoms and the action: legs weakening or giving way, falls, difficulty walking, new trouble passing urine or opening the bowels, numbness around the bottom or genitals, spreading numbness, or breathlessness. He should go to A and E or call 999 and not wait for the surgery. Ask him to repeat it back.
●Follow up: NG239 advises a first review at 3 months or earlier depending on severity. GP review after the acute assessment, to check the regimen is being continued, repeat bloods, review diet (a vegetarian diet needs a reliable B12 source) and review his support and use.

Common Mistakes in This Station

●Accepting the trainer theory and prescribing a cream or advising different shoes.
●Not asking about recreational drug use, so the diagnosis is never reached.
●Offering a routine appointment, or waiting for B12 or blood count results before acting, when both can be normal.
●Starting folic acid, or oral B12 alone, instead of intramuscular hydroxocobalamin.
●Asking him to test his own balance or reflexes on screen.
●Telling him nitrous oxide is legal, or threatening to report him.
●Advising cutting down only, or suggesting B12 tablets make continued use safe.
●Safety netting with "come back if it gets worse".
●Ignoring his fear about his mother and offering no support to stop.

Mapped to the RCGP curriculum topic: Smoking, Alcohol and Substance Misuse.

← Back to Free SCA Practice Cases