Classification of Hypersensitivity Reactions

Hypersensitivity reactions are classified into four types according to the Gell and Coombs classification. Type I, also known as anaphylactic hypersensitivity, occurs when an antigen reacts with IgE bound to mast cells. This type of reaction is responsible for anaphylaxis and atopy, such as asthma, eczema, and hay fever. Type II, or cytotoxic hypersensitivity, happens when cell-bound IgG or IgM binds to an antigen on the cell surface. This type of reaction is associated with autoimmune hemolytic anemia, ITP, Goodpasture’s syndrome, and other conditions. Type III, or immune complex hypersensitivity, occurs when free antigen and antibody (IgG, IgA) combine to form immune complexes. This type of reaction is responsible for serum sickness, systemic lupus erythematosus, post-streptococcal glomerulonephritis, and extrinsic allergic alveolitis. Type IV, or delayed hypersensitivity, is T-cell mediated and is responsible for tuberculosis, graft versus host disease, allergic contact dermatitis, and other conditions.

In recent times, a fifth category has been added to the classification of hypersensitivity reactions. Type V hypersensitivity occurs when antibodies recognize and bind to cell surface receptors, either stimulating them or blocking ligand binding. This type of reaction is associated with Graves’ disease and myasthenia gravis. Understanding the different types of hypersensitivity reactions is important in diagnosing and treating various conditions. Proper identification of the type of reaction can help healthcare professionals provide appropriate treatment and management strategies.

Keratitis is characterized by symptoms such as a red eye, sensitivity to light, and a feeling of grittiness in the eye.

Understanding Keratitis: Inflammation of the Cornea

Keratitis is a condition that refers to the inflammation of the cornea. While conjunctivitis is a common eye infection that is not usually serious, microbial keratitis can be sight-threatening and requires urgent evaluation and treatment. The causes of keratitis can vary, with bacterial infections typically caused by Staphylococcus aureus and Pseudomonas aeruginosa commonly seen in contact lens wearers. Fungal and amoebic infections can also cause keratitis, with acanthamoebic keratitis accounting for around 5% of cases. Parasitic infections such as onchocercal keratitis can also cause inflammation of the cornea.

Other factors that can cause keratitis include viral infections such as herpes simplex keratitis, environmental factors like photokeratitis (e.g. welder’s arc eye), and exposure keratitis. Clinical features of keratitis include a red eye with pain and erythema, photophobia, a foreign body sensation, and the presence of hypopyon. Referral is necessary for contact lens wearers who present with a painful red eye, as an accurate diagnosis can only be made with a slit-lamp examination.

Management of keratitis involves stopping the use of contact lenses until symptoms have fully resolved, as well as the use of topical antibiotics such as quinolones. Cycloplegic agents like cyclopentolate can also be used for pain relief. Complications of keratitis can include corneal scarring, perforation, endophthalmitis, and visual loss. Understanding the causes and symptoms of keratitis is important for prompt diagnosis and treatment to prevent serious complications.

For a newly diagnosed patient with hypertension who is under 55 years old and has stage 2 hypertension, it is recommended to add either an ACE inhibitor or an angiotensin receptor blocker. This is in accordance with the NICE guidelines, which suggest that antihypertensive drug treatments should be offered to individuals of any age with stage 2 hypertension. If the patient is 55 years or older, a calcium channel blocker like amlodipine is recommended instead.

NICE Guidelines for Managing Hypertension

Hypertension, or high blood pressure, is a common condition that can lead to serious health problems if left untreated. The National Institute for Health and Care Excellence (NICE) has published updated guidelines for the management of hypertension in 2019. Some of the key changes include lowering the threshold for treating stage 1 hypertension in patients under 80 years old, allowing the use of angiotensin receptor blockers instead of ACE inhibitors, and recommending the use of a calcium channel blocker or thiazide-like diuretic in addition to an ACE inhibitor or angiotensin receptor blocker.

The guidelines also provide a flow chart for the diagnosis and management of hypertension. Lifestyle advice, such as reducing salt intake, caffeine intake, and alcohol consumption, as well as exercising more and losing weight, should not be forgotten and is frequently tested in exams. Treatment options depend on the patient’s age, ethnicity, and other factors, and may involve a combination of drugs.

NICE recommends treating stage 1 hypertension in patients under 80 years old if they have target organ damage, established cardiovascular disease, renal disease, diabetes, or a 10-year cardiovascular risk equivalent to 10% or greater. For patients with stage 2 hypertension, drug treatment should be offered regardless of age. The guidelines also provide step-by-step treatment options, including adding a third or fourth drug if necessary.

New drugs, such as direct renin inhibitors like Aliskiren, may have a role in patients who are intolerant of more established antihypertensive drugs. However, trials have only investigated the fall in blood pressure and no mortality data is available yet. Patients who fail to respond to step 4 measures should be referred to a specialist. The guidelines also provide blood pressure targets for different age groups.

The chance of Down syndrome increases with maternal age:
Age (years) Chance
20 1:1500
30 1:800
35 1:270
40 1:100
>45 >1:50

Therefore, the correct answer is 1 in 100.

If a woman over the age of 30 presents with an unexplained breast lump, it is important to refer her urgently to the breast team using a suspected cancer pathway referral. It is important to inform the patient that they are being referred to a cancer service, but also explain that not all referrals to cancer services result in a cancer diagnosis. It is incorrect to perform a biopsy as an initial investigation, as this will be done in secondary care. While fibroadenoma is a common cause of breast lumps in young women, urgent referral to the breast team is necessary to rule out cancer in patients over 30 years old. It is not appropriate to schedule a GP review in 2 weeks, as this lump needs prompt investigation by the breast team.

In 2015, NICE released guidelines for referring individuals suspected of having breast cancer. If a person is 30 years or older and has an unexplained breast lump with or without pain, or if they are 50 years or older and have discharge, retraction, or other concerning changes in one nipple only, they should be referred using a suspected cancer pathway referral for an appointment within two weeks. If a person has skin changes that suggest breast cancer or is 30 years or older with an unexplained lump in the axilla, a suspected cancer pathway referral should also be considered. For individuals under 30 years old with an unexplained breast lump with or without pain, non-urgent referral should be considered.

The use of allopurinol in combination with azathioprine can increase the risk of myelosuppression and neutropenic sepsis. This is because azathioprine is metabolized to its active form, 6-mercaptopurine, which is then metabolized by xanthine oxidase. Allopurinol inhibits xanthine oxidase, leading to an accumulation of 6-mercaptopurine and an increased risk of myelosuppression. Chronic alcohol use and omeprazole use do not significantly increase the risk of myelosuppression when used with azathioprine or allopurinol.

Allopurinol is a medication used to prevent gout by inhibiting xanthine oxidase. Traditionally, it was believed that urate-lowering therapy (ULT) should not be started until two weeks after an acute attack to avoid further attacks. However, the evidence supporting this is weak, and the British Society of Rheumatology (BSR) now recommends delaying ULT until inflammation has settled to make long-term drug decisions while the patient is not in pain. The initial dose of allopurinol is 100 mg once daily, with the dose titrated every few weeks to aim for a serum uric acid level of less than 300 µmol/l. Colchicine cover should be considered when starting allopurinol, and NSAIDs can be used if colchicine cannot be tolerated. ULT is recommended for patients with two or more attacks in 12 months, tophi, renal disease, uric acid renal stones, prophylaxis if on cytotoxics or diuretics, and Lesch-Nyhan syndrome.

The most significant adverse effects of allopurinol are dermatological, and patients should stop taking the medication immediately if they develop a rash. Severe cutaneous adverse reaction (SCAR), drug reaction with eosinophilia and systemic symptoms (DRESS), and Stevens-Johnson syndrome are potential risks. Certain ethnic groups, such as the Chinese, Korean, and Thai people, are at an increased risk of these dermatological reactions. Patients at high risk of severe cutaneous adverse reaction should be screened for the HLA-B *5801 allele. Allopurinol can interact with other medications, such as azathioprine, cyclophosphamide, and theophylline. Azathioprine is metabolized to the active compound 6-mercaptopurine, which is oxidized to 6-thiouric acid by xanthine oxidase. Allopurinol can lead to high levels of 6-mercaptopurine, so a much-reduced dose must be used if the combination cannot be avoided. Allopurinol also reduces renal clearance of cyclophosphamide, which may cause marrow toxicity. Additionally, allopurinol causes an increase in plasma concentration of theophylline by inhibiting its breakdown.

Understanding Obesity in Children

Childhood obesity is a complex issue that requires careful assessment and management. Unlike adults, defining obesity in children is more challenging as body mass index (BMI) varies with age. To accurately assess BMI, percentile charts are needed. According to recent guidelines by the National Institute for Health and Care Excellence (NICE), the UK 1990 BMI charts should be used to provide age- and gender-specific information.

NICE recommends tailored clinical intervention if BMI is at the 91st centile or above. If BMI is at the 98th centile or above, assessing for comorbidities is necessary. Lifestyle factors are the most common cause of obesity in childhood. However, other factors such as growth hormone deficiency, hypothyroidism, Down’s syndrome, Cushing’s syndrome, and Prader-Willi syndrome can also contribute to obesity in children.

Obesity in children can lead to various consequences, including orthopaedic problems such as slipped upper femoral epiphyses and Blount’s disease, musculoskeletal pains, psychological consequences like poor self-esteem and bullying, sleep apnoea, and benign intracranial hypertension. Moreover, obesity in childhood can increase the risk of developing type 2 diabetes mellitus, hypertension, and ischaemic heart disease in the long run. Therefore, it is crucial to identify and manage obesity in children to prevent these adverse outcomes.

Differential Diagnosis for a Patient with Low Mood and Renal Stones

Primary Hyperparathyroidism:
This condition can cause hypercalcemia, which may present as renal stones, osteoporosis, arthritis, nausea and vomiting, peptic ulcer disease, constipation, polyuria, depression, memory loss, and delirium.

Hyperthyroidism:
Hyperthyroidism may present with restlessness, irritability, insomnia, tremor, palpitations, weight loss, sweating, heat intolerance, diarrhea, oligomenorrhea, hair thinning, and muscle weakness. Graves’ disease may also cause a goiter and thyroid eye disease, presenting as proptosis, dry eyes, periorbital edema, and lagophthalmos.

Hypothyroidism:
Typical features of hypothyroidism include dry skin, brittle and diminished hair, lethargy, cold intolerance, dull or blank expression, puffy eyelids, and weight gain. Patients may also experience cerebellar ataxia, ascites, non-pitting edema of the hands and feet, and congestive cardiac failure.

Pseudopseudohypoparathyroidism:
This condition may present with short fourth and fifth metacarpals, round face, short stature, basal ganglia calcification, and decreased IQ.

Secondary Hyperparathyroidism:
This condition may present with signs and symptoms of hypocalcemia, including perioral paresthesia, seizures, spasms, anxiety, increased smooth muscle tone, disorientation, dermatitis, impetigo herpetiformis, cataracts, Chvostek’s sign, and long Q–T interval.

Differential Diagnosis for a Patient with Low Mood and Renal Stones

It is probable that the patient is suffering from malignant otitis externa, a condition that affects individuals with weakened immune systems like those with diabetes. This condition is characterized by osteomyelitis of the temporal bone. Despite receiving several rounds of antibiotic drops, the patient’s symptoms have not improved. It is recommended that the patient be referred to an ENT specialist for a CT scan of the temporal bones and treated with an extended course of intravenous antibiotics.

Understanding Otitis Externa: Causes, Features, and Management

Otitis externa is a common condition that often prompts patients to seek medical attention. It is characterized by ear pain, itch, and discharge, and is caused by various factors such as infection, seborrhoeic dermatitis, and contact dermatitis. Swimming is also a common trigger of otitis externa. Upon examination, the ear canal appears red, swollen, or eczematous.

The recommended initial management of otitis externa involves the use of topical antibiotics or a combination of topical antibiotics with a steroid. However, if the tympanic membrane is perforated, aminoglycosides are traditionally not used. In cases where there is canal debris, removal may be necessary, while an ear wick may be inserted if the canal is extensively swollen. Second-line options include oral antibiotics, taking a swab inside the ear canal, and empirical use of an antifungal agent.

It is important to note that if a patient fails to respond to topical antibiotics, referral to an ENT specialist may be necessary. Malignant otitis externa is a more serious condition that is more common in elderly diabetics. It involves the extension of infection into the bony ear canal and the soft tissues deep to the bony canal, and may require intravenous antibiotics.

Overall, understanding the causes, features, and management of otitis externa is crucial in providing appropriate care and preventing complications.

Motor neurone disease often presents with spared eye movements. This is particularly common in cases of bulbar-onset amyotrophic lateral sclerosis (ALS), where patients may struggle with swallowing liquids more than solids in the early stages. Other symptoms may include facial weakness, hypophonic speech, fasciculations, and reduced jaw jerk reflex (a lower motor neuron sign). In contrast, achalasia typically causes difficulty swallowing both liquids and solids due to a loss of normal peristalsis and failure of the lower sphincter to relax during swallowing. This condition does not typically involve fasciculation of the tongue. Oesophageal carcinoma may also cause difficulty swallowing, but patients usually report difficulty with solids before liquids and may experience constitutional symptoms such as weight loss.

Understanding Motor Neuron Disease: Signs and Diagnosis

Motor neuron disease is a neurological condition that affects both upper and lower motor neurons. It is a rare condition that usually presents after the age of 40 and can manifest in different patterns such as amyotrophic lateral sclerosis, progressive muscular atrophy, and bulbar palsy. The diagnosis of motor neuron disease is based on clinical features, including the presence of fasciculations, the absence of sensory signs, and the combination of upper and lower motor neuron signs. Wasting of the small hand muscles and tibialis anterior is also common.

Other features that can help diagnose motor neuron disease include the absence of external ocular muscle involvement, the absence of cerebellar signs, and preserved abdominal reflexes. Sphincter dysfunction, if present, is usually a late feature. While vague sensory symptoms may occur early in the disease, sensory signs are typically absent.

Nerve conduction studies can help exclude a neuropathy, while electromyography shows a reduced number of action potentials with increased amplitude. MRI is usually performed to exclude other conditions such as cervical cord compression and myelopathy. Understanding the signs and diagnosis of motor neuron disease is crucial for early detection and management of the condition.