35
ausdoc. com. au 13 FEBRUARY 2026
35
SPOT DIAGNOSIS
MORE QUIZZES ONLINE
Available at: ausdoc. com. au / spot-diagnosis
Professor Dedee Murrell Head of dermatology, St George Hospital; professor, faculty of medicine, UNSW Sydney; and honorary professorial fellow, The George Institute for Global Health, Sydney, NSW. Co-authors: Alvin Leung, medical student at the University of Bristol; and Dr Nasim Niknezhad, a medical dermatology fellow at Premier Specialists and St George Hospital, Sydney, NSW.
Shed some light on this dark spot
A 60-YEAR-old Caucasian female presents with a dark spot on the third toe of her left foot. The lesion is located on the frontal aspect of the skin under the nail. It is completely asymptomatic, and owing to its unusual location, the patient is unsure how long the lesion has been present. She only recalls having had a pedicure a week ago and experiencing pain when her nail was being clipped.
On examination, there is a well-demarcated, irregularly shaped pigmented macule. Under dermoscopy( pictured), the macule has a brown colouration with a homogeneous pattern. Both localised and satellite globules can also be seen. exposure or moderate-level chronic exposure can result in irreversible injury to the nervous system, kidneys and other organs. 1
Lead is absorbed through the lungs, gastrointestinal tract and, to a lesser extent, the skin. Up to 95 % of the body’ s lead stores are held in the bones, with a half-life of decades. 1
Once absorbed, lead can cross the blood – brain barrier and affect cerebral regions responsible for memory and cognition. Lead interferes with calcium-dependent cellular processes and causes excessive calcium accumulation, mitochondrial dysfunction and the release of reactive oxygen species, leading to neuronal death. 2 The neurotoxic impact can result in memory loss, motor impairment, irritability, aggression and cognitive decline over time. 3
Other manifestations of chronic lead exposure
include gastrointestinal( abdominal pain, constipation, weight loss, nausea, anorexia), renovascular( hypertension, nephropathy), musculoskeletal( myalgia, arthralgia, hyperuricaemia, gout) and haemotological features( chronic anaemia). 1
In adults, occupational exposure is the most common source, particularly among those who work in the production of lead – acid batteries or pipes, metal recycling and foundries. 1, 4 Hobbies that involve potential exposure include glazed pottery making; lead soldering; preparing lead shot or fishing sinkers; leadlight making; and renovation and restoration of older homes, boats or cars. 1, 5
Assessment of serum lead is key to diagnosis. Other suggestive features on pathology include a normocytic normochromic anaemia and basophilic stippling on FBC.
In this case, poorly controlled diabetes may have compounded the cognitive effects of chronic lead exposure.
Treatment of lead toxicity requires specialist toxicology input, including consideration for chelation therapy. Removal of the causative source and ongoing prevention from re-exposure are crucial.
This case emphasises the importance of considering environmental and hobbyist exposures in cognitive decline, particularly when standard evaluations are inconclusive. Lead toxicity— along with other metals, such as manganese and cadmium— warrants consideration in those with potential exposures and unexplained cognitive or multisystem symptoms.
Clinicians should also consider the additive effects of poorly controlled diabetes on cognitive health, highlighting the importance of comprehensive management for both metabolic and environmental factors.
Lead is absorbed through the lungs, gastrointestinal tract and skin. Up to 95 % of the body’ s lead stores are held in the bones, with a half-life of decades.
Management and outcome
Andy is urgently referred to a tertiary hospital for toxicology and neurological review and further management. Chelation therapy is not warranted, so the plan is for Andy to avoid further lead exposure, as well as follow-up serum lead testing and cognitive assessments. 6
Six months later, cognitive assessment demonstrates an 80 % improvement in memory. There is no evidence of long-term neurological damage on MRI.
Andy is advised to cease using lead in his hobbies and to switch to non-toxic materials, such as copper. His diabetes management is also intensified to improve glycaemic control through the uptitration of metformin – empagliflozin to maximum dose and the addition of sitagliptin and gliclazide. He is able to return to full-time work.
References on request from kate. kelso @ adg. com. au
The patient’ s work was so significantly impacted that he had to take time off.
Have an interesting clinical case?
Log CPD hours for preparing educational content for publication.
We pay $ 400 for each published case.
For details, email medical editor kate. kelso @ adg. com. au
Which is the most likely diagnosis? a Benign acral melanocytic naevus b Acral melanoma c Subcorneal haematoma d Subungual haematoma
Have an interesting
Spot Diagnosis?
Log CPD hours for preparing educational content for publication.
We pay $ 100 for each published quiz.
For details, email medical editor kate. kelso @ adg. com. au
ANSWER The answer is C. Subcorneal haematomas, also referred to as calcaneal petechiae, or talon noir when found on the heel, represent collections of blood in the stratum corneum resulting from capillary rupture in the papillary dermis. They are typically trauma related and are most commonly observed on the palms and soles of athletes. In this case, the lesion was most likely caused by a careless pedicurist.
It may be hard to distinguish subcorneal haematomas from important differentials— such as acral melanoma and benign acral melanocytic naevus— macroscopically; therefore, dermoscopic examination and clinical correlation are essential. On dermoscopy, subcorneal haematomas are typically red – black or brown in colour with homogeneous, globular and / or parallel ridge patterns. Other distinguishing features include satellite globules corresponding to the sites of capillary rupture, as well as a well-defined border as the blood clots. In addition to dermoscopy, another simple diagnostic test is to pare the lesion with a sterile scalpel. In subcorneal haematomas, this removes the overlying stratum corneum and the haematoma beneath it, leading to complete resolution of the pigmentation.
The lesion in this case does not resemble a benign acral melanocytic naevus as it does not have the characteristic parallel furrows or lattice-like patterns that distribute throughout the lesion.
Lesions that raise suspicion of an acral melanoma typically demonstrate irregular pigment networks, such as irregular asymmetrical blotching and thick parallel ridges, with or without areas of regression on dermoscopy. These features are not seen in this case.
This is not a subungual haematoma because the blood collection is within the skin below the nail rather than between the nail and the nail bed.