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Pit your wits against these underarm patches
ausdoc. com. au 31 OCTOBER 2025
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Time in Ranges
Glucose Metrics
Average Glucose
Goal: < 8.5 % mmol / L
Goals for type 1 and Type 2 Diabetes
Each 5 % increase in the Target Range is clinically beneficial Each 1 % time in range = about 15 minutes per day
14 % Very High
Goal: < 5 %
28 % High
57 % In Range
Goal: > 70 %
1 % Low < 1 % Very Low
Goal: < 1 %
Target Range: 3.9-10.0 mmol / L Very High: Above 13.9 mmol / L Very Low: Below 3.0 mmol / L
42 %
Goal: < 25 %
1 %
Goal: < 4 %
9.7 mmol / L
GMI
7.5 %
Goal: < 7 %
Coefficient of Variation
35.9 %
Goal: < 36 %
Time CGM Active
99.0 %
Figure 3: Kaye’ s continuous glucose monitoring( CGM) averages for the twoweek period post-hybrid closed loop insulin pump.
MORE ON THIS DIAGNOSIS ONLINE ausdoc. com. au / spot-diagnosis
SPOT DIAGNOSIS
Pit your wits against these underarm patches
JESS is a 43-year-old woman who presents with a one-month history of mildly itchy patches in both axillae. The lesions began as red-brown macules and gradually expanded, merging into larger patches. Jess has trialled a topical antifungal, with no improvement. She is overweight and has hypertension and type 2 diabetes— both well controlled with lifestyle measures, an ACEI and metformin.
On examination, there are well-defined, wrinkled, erythematous-brownish plaques with minimal scaling in both axillae( pictured on left). Wood’ s lamp examination findings are also pictured( right). No other lesions or lymphadenopathy was noted.
Photo reproduced from BMJ, Hu H, Liu C, Li Q, Li J., 389: e081933, 2025 with permission from BMJ Publishing Group Ltd.
Which is the most likely diagnosis? a Erythrasma b Inverse psoriasis c Acanthosis nigricans d Candidiasis
Figure 4: Kaye’ s continuous glucose monitoring averages for the two-week period post-hybrid closed loop insulin pump.
BSLs. However, a high evening BSL will continue throughout sleep without user intervention, resulting in a high fasting BSL. Sleep activity-enabled devices include an algorithm to optimise glycaemic control during scheduled sleep hours, using intense basal titration only, aiming to maintain a BSL between 6.2-6.7mmol / L. If achieved, this can significantly increase a user’ s overall TIR. 3
HCL devices that offer sleep activity allow the option for the mode to be activated manually or programmed. For best results, it is suggested the mode be programmed to function for 6-8 hours, generally initiated at a time at which the user is no longer eating or active. 3
The impact of devices which offer algorithm adjustment for sleep has potential to reach beyond improved glycaemic control to encompass improvements in psychosocial factors. Anecdotally, users report immediate and significant improvements in sleep quality and flow-on benefits from waking with their BSL in target range, and there is some empirical data to back this. 4, 8
Outcome
In the two weeks after starting the HCL system, Kaye’ s CGM estimated HbA1c is 7.5 % and her TIR is 57 %( see figure 3).
There is a significant improvement in Kaye’ s overnight and fasting glycaemia( see figure 4).
Kaye is still experiencing significant post-meal hyperglycaemia at dinner, indicating her dinner bolusing habits have not changed. However, by 1-2am, the sleep activity algorithm has her SGL within the target range. The flow-on effect is seen across the day, with average BSL remaining within target range during the period in which Kaye is more accurately taking bolus insulin doses with breakfast and lunch. Furthermore, now that Kaye is approaching the dinner meal with a BSL within target, the average post-dinner BSL has also reduced.
Kaye also reports feeling much better upon waking. She no longer feels exhausted and in fact, feels as well as she has since before her diabetes diagnosis.
Conclusion
Options for management of type 1 diabetes have advanced substantially in recent years. Systems that integrate insulin infusion with CGM are now widely used, and HCL systems offer the potential to improve glycaemic control and quality of life even further. The development of systems with the capacity to adapt for a wider variety of predictable factors in day-to-day life, such as activity and sleep, offers even greater potential to further improve both glycaemic control and essential contributors to quality of life, such as sleep. 5
References on request from kate. kelso @ adg. com. au
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Spot Diagnosis?
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ANSWER The answer is a. Erythrasma is a superficial skin infection caused by gram-positive, non-spore-forming, aerobic or facultative bacilli Corynebacterium minutissimum. Erythrasma typically presents with erythematous scaly plaques or patches in intertriginous areas. Plaques have a telltale wrinkled cigarette paper – like appearance, with superficial fissuring. In those with darker skin, there is minimal scaling and lesions are more likely to appear as darker-brown or red-brown patches, with marked post-inflammatory pigmentation. Coral-red fluorescence on Wood’ s lamp examination is a hallmark finding as a result of coproporphyrin III released by the bacteria. If the skin has been washed recently before examination, fluorescence may not be evident because the porphyrin responsible is water soluble. 1, 2
Risk factors for the condition include living in humid climates, excessive sweating, obesity, diabetes and advancing age. 1, 2 Diagnosis is clinical, based on appearance and characteristic Wood’ s lamp examination findings. Skin swab, scrapings or biopsy may aid diagnosis if in doubt. Erythrasma is usually self-limiting, although it can be complicated by contact dermatitis, lichenification, post-inflammatory pigmentation and co-infection with other bacteria, yeasts and dermatophytes. Serious complications are very rare.
Corynebacteria have been reported to causes abscess, cellulitis, cutaneous granuloma, endocarditis, pyelonephritis, endophthalmitis, arteriovenous fistula infection and meningitis. 2 Treatment is typically with topical antibiotic therapy( clindamycin, fusidic acid, mupirocin or benzoic acid with salicylic acid); oral antibiotics( erythromycin or tetracyclines) are reserved for complicated cases. Preventive measures to keep the skin clean and dry can help reduce recurrence. 1
Inverse psoriasis is characterised by erythematous nonscaly plaques in intertriginous regions that do not fluoresce on Wood’ s lamp examination. 1, 3
Acanthosis nigricans is characterised by dark-brown hyperpigmentation, local skin thickening and a velvety texture— often with associated papillomatous growths and deep skin markings. It also does not fluoresce on Wood’ s lamp examination. 1, 3 Candidiasis typically causes red plaques with satellite lesions and occasionally white or yellow discharge. Wood’ s lamp examination is typically negative. 1, 3
Dr Kate Kelso is a GP and medical editor at Australian Doctor. References on request from kate. kelso @ adg. com. au