Introduction
Acromegaly is one of those classic “spot the diagnosis” conditions that examiners love. Its slow, insidious onset means patients often present with years of symptoms, and the clinical signs can be striking if you know what to look for. For the UKMLA, a clear understanding of the acromegaly diagnosis UKMLA pathway is crucial. This high-yield guide will walk you through the 3 essential steps to identify the condition. We’ll cover the clinical features, the definitive biochemical tests, and the essential imaging, ensuring you can tackle any related question with confidence.
What is Acromegaly and Why is it a Classic UKMLA Topic?
Acromegaly is a rare endocrine disorder caused by the excessive production of growth hormone (GH) in adulthood, after the fusion of the epiphyseal plates in the skeleton. It’s a key topic in UKMLA endocrinology essentials because it tests a perfect combination of clinical observation, logical investigation, and understanding of hormonal feedback loops. For a more detailed patient-level overview, the Society for Endocrinology provides excellent resources on Acromegaly.
The Pathophysiology Simplified: Excess Growth Hormone (GH)
In adulthood, GH doesn’t make you taller. Instead, it promotes the growth of soft tissues, cartilage, and bone, leading to the characteristic features of the condition. GH also has significant metabolic effects, including increasing glucose levels and promoting insulin resistance, which is why a significant number of patients with acromegaly also have diabetes mellitus.
The Role of the Pituitary Adenoma
In over 95% of cases, acromegaly is caused by a benign tumour of the pituitary gland called a pituitary adenoma. This tumour autonomously secretes large amounts of growth hormone, ignoring the body’s normal negative feedback mechanisms. As the tumour grows, it can also compress surrounding structures, most notably the optic chiasm, leading to specific visual field defects.
Step 1: Recognising the Clinical Features (The “Spot Diagnosis”)
The first step in achieving an acromegaly diagnosis for UKMLA questions is clinical suspicion. The changes are gradual, so patients and their families may not notice them for years. A classic exam vignette might involve a patient presenting their old passport or driving licence, showing a dramatic change in their facial features. A sharp UKMLA clinical examination is key.
Classic Facial and Acral Changes
Coarsening of facial features: Prominent brow (frontal bossing), large nose, and thick lips.
Prognathism: Protrusion of the lower jaw.
Macroglossia: Enlarged tongue, which can cause obstructive sleep apnoea.
Acral enlargement: Increased size of hands and feet (patients report needing larger rings, gloves, or shoes).
Spade-like hands: Broad, thick hands.
Systemic Manifestations You Must Know
Cardiovascular: Hypertension, cardiomyopathy, and heart failure are major causes of mortality.
Metabolic: Type 2 diabetes mellitus or impaired glucose tolerance.
Musculoskeletal: Arthralgia and carpal tunnel syndrome are very common.
Integumentary: Oily skin, skin tags, and excessive sweating (hyperhidrosis).
Symptoms the Patient Might Report
Headaches (due to the tumour itself)
Excessive sweating
Snoring or diagnosed sleep apnoea
Joint pain
Tingling in the hands (carpal tunnel syndrome)
Change in vision
Step 2: The Crucial Biochemical Investigations
Once you suspect acromegaly, the diagnosis must be confirmed with specific blood tests. Following established clinical guidelines, such as those summarised by the Mayo Clinic on Acromegaly Diagnosis, is crucial.
The First-Line Test: Insulin-like Growth Factor 1 (IGF-1)
Measuring a random GH level is useless because GH is secreted in a pulsatile manner. The best initial screening test is a serum IGF-1 level. GH stimulates the liver to produce IGF-1, which has a much longer half-life and provides a stable reflection of the average GH level over the past 24 hours.
Blockquote: If a patient has clinical features of acromegaly, a raised, age-adjusted IGF-1 level makes the diagnosis highly likely and mandates further investigation. A normal IGF-1 level effectively rules out the condition.
The Definitive Diagnostic Test: The Oral Glucose Tolerance Test (OGTT)
The gold standard for confirming acromegaly is the Oral Glucose Tolerance Test (OGTT) with serial GH measurements.
The Principle: In a healthy person, a large glucose load will suppress GH secretion. In a patient with acromegaly, the pituitary adenoma continues to secrete GH autonomously, so it fails to suppress.
The Procedure: A baseline GH level is taken, the patient drinks a 75g glucose solution, and GH levels are measured at 30, 60, 90, and 120 minutes.
Interpretation: The key is the “nadir” or lowest GH level achieved during the test. A failure of GH to suppress to below a certain level (typically <1 µg/L, but local lab values may vary) confirms the diagnosis of acromegaly.
Step 3: Localising the Tumour with Imaging
After biochemical confirmation, the final step is to find the source of the excess GH.
MRI of the Pituitary: The Gold Standard
An MRI scan of the pituitary gland with contrast is the investigation of choice. This will identify the pituitary adenoma, determine its size (microadenoma <1cm, macroadenoma >1cm), and show if it is compressing any nearby structures.
Visual Field Testing: Assessing for Optic Chiasm Compression
Any patient with a pituitary macroadenoma, especially if it is shown to be near the optic chiasm on MRI, must have formal visual field testing (e.g., using a Humphrey visual field analyser). The classic defect caused by compression of the optic chiasm is a bitemporal hemianopia (loss of the outer half of the visual field in both eyes).
Putting It All Together: A UKMLA-Style Case Example
A 45-year-old man presents to his GP complaining of headaches and excessive sweating. He mentions that his wedding ring no longer fits and he has had to buy larger shoes twice in the last three years. His wife notes he snores very loudly. On examination, you note prominent frontal bossing and a large jaw.
Step 1 (Suspicion): The combination of acral enlargement, sweating, and coarse facial features strongly suggests acromegaly. This is one of the frequently tested topics on the UKMLA AKT.
Step 2 (Biochemical Confirmation): You would order a serum IGF-1 level. If raised, you would refer him to an endocrinologist for a confirmatory OGTT.
Step 3 (Localisation): After the OGTT confirms a non-suppressible GH level, an MRI of his pituitary would be performed to identify the adenoma. This completes the acromegaly diagnosis UKMLA pathway.
Frequently Asked Questions (FAQ) about Acromegaly Diagnosis
GH is released in pulses, so a single random measurement is unreliable. Its level can be high one minute and low the next. IGF-1 is stable and reflects the 24-hour average GH production, making it a much better screening test.
Gigantism is caused by the same process (excess GH from a pituitary adenoma) but occurs in children and adolescents before their bone growth plates have fused. This leads to excessive linear growth and very tall stature.
Normal IGF-1 levels are highest during puberty and gradually decline with age. Therefore, a patient’s result must be compared to the normal reference range for their specific age group.
Pregnancy and severe liver or kidney disease can affect IGF-1 levels, but in the context of the classic clinical features, a raised IGF-1 is highly specific for acromegaly.
Bitemporal hemianopia, due to the pituitary tumour growing upwards and compressing the optic chiasm from below.
Over 95% do. Very rarely, it can be caused by ectopic tumours (e.g., in the lung or pancreas) producing GH or GHRH (Growth Hormone-Releasing Hormone), but for exam purposes, you should always assume a pituitary source unless told otherwise.
To normalise GH and IGF-1 levels, reduce the size of the tumour, relieve any mass effect, and manage the comorbidities (like diabetes and hypertension). The acromegaly diagnosis is the first step in this process.
If left untreated, yes. The mortality rate is 2-3 times higher than the general population, primarily due to cardiovascular disease. Successful treatment can normalise this risk.
A large pituitary adenoma can compress the normal pituitary tissue, causing deficiencies in other hormones (hypopituitarism). It’s essential to check a full pituitary profile, including TSH, ACTH, LH/FSH, and prolactin.
The procedure is the same (75g glucose drink), but the purpose is different. For diabetes, you are measuring glucose levels to check for insulin resistance. For acromegaly, you are measuring GH levels to check for failure of suppression.
Conclusion: Key Diagnostic Takeaways for Your Exam
Diagnosing acromegaly for the UKMLA is a test of logical progression. By using the 3-step framework—Spot the features, Confirm with tests, Localise the source—you can structure your thinking and arrive at the correct answer. Remember the key investigations: IGF-1 first, then the OGTT for confirmation, followed by an MRI. Understanding this pathway demonstrates a high level of clinical acumen that aligns perfectly with the GMC UKMLA content map. Master these steps, and you will be fully prepared for any acromegaly diagnosis UKMLA question on your exam.
