This set of patients represents a small cohort (n = 27) of a population from an urban area with a high ethnic mix. Interestingly, despite the wide ethnic diversity of the local area, a high proportion of this cohort were white (69%). Despite the wide spread of ages (35 – 96), the average age of the patient in this study was 62.6 years which concurs with similar studies[26
] that ALM is most frequent in the 60–70 age group[25
]. ALM appears to occur in an older age group, other types of melanoma having a peak incidence around 50 years of age, albeit with a wider age spread[2
]. The female preponderance to ALM was 2.8:1 slightly higher than other published data [26
] but still confirms that MM is a disease more common in females[3
Within this study, the prime location for ALM was the plantar surface (65%), with 4 of these occurring under the first metatarsal head. A smaller number were seen in nail beds, ankle and dorsum of the foot. A similar prevalence pattern for the plantar area has been reported by Soon et al[27
](61%) and Kuchelmeister[25
] (65%) with sub-ungual lesions making up a smaller percentage of all cases of ALM. The four sub-ungual tumours in this study were located exclusively on the hallux (50%) and fifth toe (50%). The hallux has been consistently reported to be the most common area for sub-ungual lesions in the foot. Possible reasons for this are two-fold. Firstly, the hallux may be the most prevalent location owing to the larger proportion of nail tissue in this area. Secondly, one could debate the role of trauma. The hallux is typically an area of the forefoot more prone to abuse from footwear and one-off injury. In one case series from Germany, 6 patients with ALM reported tight footwear as a possible causative agent[23
]. The authors went on to discuss that patients with acral melanoma tended to report a high rate of trauma compared to those with melanoma at other sites but this was not found to be statistically significant. Furthermore, one could hypothesize, if physical trauma was associated with melanoma, one would expect the foot show a more significant proportion of lesions on the foot as a result of the forces of weight bearing and locomotion.
Early recognition is the key to improving survival rates[29
]. As cutaneous melanoma is a visible disease, both the patient and practitioner play a major role in recognising suspicious lesions. Initially, the time taken to reach a diagnosis depends on the patient's ability to recognise and seek professional advice. Secondly, diagnosis depends on the professional's capacity to recognise the lesion. Data were available for 19 patients showing that the time from first noticing a lesion to diagnosis ranged from 1 – 36 months, which shows similarities to other studies of patients with ALM[26
]. Reasons for the delay were not examined in this study but have been reviewed by Richard et el[30
]. In a series of 590 patients they examined the reasons for delay in melanoma diagnosis and discovered that male gender, increasing age and a low educational level were all risk factors for a later presentation to physicians. In a second paper[31
] examining physician delays, acral locations and lack of lesion pigmentation were factors more likely to lead to a delay in diagnosis by a physician, particularly lesions in acral locations without pigmentation.
Within this study, symptoms or initial diagnoses were recorded for 21 patients. The most common reported symptom was a change in the size of the lesion (38%) followed by bleeding (19%), change in colour (9%) and change lesion form (becoming raised/nodular) (9%). Bleeding is a common feature in melanoma which have entered a vertical growth phase and have become ulcerated[2
] and may represent a feature of advanced disease. The average lesion thickness in patients reporting bleeding was significantly higher in those not reporting it (mean thickness 6.13 mm v 3.8 mm) although due to the small numbers involved it was difficult to draw firm conclusions.
Seven of the twenty one lesions (33%) were initially misdiagnosed as other conditions (warts, a fungal infection, haematoma and an ulcer). Numerous papers have highlighted conditions including warts, tinea pedis, ulceration, infection, paronychia, haematoma, onychomycosis, ischaemic necrosis, pyogenic granuloma, ganglions and blisters which have been later discovered to be ALM [27
]. Misdiagnosis is a common feature of melanoma on the foot but ALM in particular has been shown to be more likely mis-diagnosed than other sub-types of the disease[37
]. Delays can in turn lead to a poorer prognosis for the patient. The misdiagnosis rate in this study was 33%, other have reported rates of between 33% – 67%[27
It is appreciated that the results of this study represent a retrospective review of patient case notes which have some inherent bias – in particular that this data was collected at a tertiary centre where possibly only more complex cases are seen. However, in view of the relative rarity of the condition, twenty-six cases represent a sizeable cohort, which has been shown to be concurrent when compared to literature on this topic.
This paper has highlighted an uncommon but serious lesion which may present for the first time to Chiropodists and Podiatrists. One third of the lesions, in the presented cohort, were seen prior to diagnosis by a chiropodist or podiatrist. Unfortunately, typical features of melanoma as exhibited by the "ABCDE" rule may not be present in a proportion of ALM and so misdiagnosis remains a significant risk. Therefore it is important to remain vigilant and where there is clinical suspicion, patients should be referred for a prompt dermatological opinion. In suggesting ways to heighten awareness, the typical patient profile should be borne in mind as well as continuing the patient health education message. In addition, dermoscopy has been demonstrated as a useful, non-invasive technique to increase sensitivity in acral lesions[39
]improving early recognition.