Occam’s Razor is a problem-solving principle that basically states that the simplest explanation is usually the right one. This rings true when a patient comes into the clinic complaining of a single, painful toenail - immediately suspicion falls on the most common causes – onychocryptosis or an involuted toenail but what about when there is no evidence of either? What next? This article looks at a few causes of a painful toenail in the absence of the obvious ingrowing toenail.
After the initial assessment of the patient, collecting the usual details, its worth getting a description of the pain – when does it hurt (during activity, in the warm or cold, at night etc.,), what makes it better? As this can be quite useful in determining the cause.
The Sub-ungual corn
Beyond the ingrowing toenail, probably the most common cause, eliciting pain when the nail is pressed is the sub-ungual (S/U) corn. Hard corns normally appear on the plantar surface or lateral side of the fifth toe but occasionally they can appear under the nail plate itself. Press the nail and the pain occurs. In 2014, we published a review of 14 cases of the S/U corns (1). Surprisingly, this was the first time it appeared in the medical literature despite it being in dusty old “chiropody” textbooks for decades! Patients are typically in their 6th or 7th decade. Lesions may be hard to visualise under the nail but 75% of the cases we reviewed were accompanied by some element of S/U haemorrhage. Also, nearly all of them were located in the distal-central axis of the toe, just under the free edge. Why they were located here was possibly explained by pressure with 100% of lesions being the highest point of the toe when viewed in a lateral profile. For most patients, simple nail resection and enucleation is enough to relieve symptoms. In our case series review, many lesions did not return even after 6 months follow up.
Glomus Tumour showing purple discolouration under dermoscopy
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A nail which is intermittently painful particularly worse when there is a change in temperature or excruciating paroxysmal pain suggests a sub-ungual glomus tumour. These are benign lesions which develop from the glomus body, particularly abundant in the sub-ungual areas of the fingers and occasionally, the toes. Most commonly observed in women, the pain can be elicited by direct touch to the affected nail (known as Love’s test) (2). Lesions can sometimes be visualised as a dark small sub-ungual area – dermoscopy can be helpful (see image above)(3). An MRI can be helpful but not always conclusive. Surgical excision is the only effective treatment for eradicating the pain.
Sub-Ungual Exostosis
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A painful toenail in an adolescent or young adult with accompanying nail changes may suggest the presence of a sub-ungual exostosis. The exostosis is typically an osteocartilaginous tumour of the distal phalanx. Visually, one may observe a red nodule in the early stage under the nail which may protrude from the free edge which is solid to the touch but blanches under pressure. As it grows localised distortion of the toenail can occur with symptoms such as involution or onychocryptosis which may disguise the diagnosis.
Lateral X Ray revealing exostosis
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Pain in the latter stages is a common feature. Diagnosis is made through a lateral X-ray of the phalanx. This can also help to distinguish the exostosis from a sub-ungual wart which can also lead to distal nail distortion as it grows. A review of 25 exostosis cases suggests this typically occurs in the hallux but can occur on the lesser toes or under fingernails. Females are most commonly affected (4). The role of trauma as a cause remains debated in the literature. Surgical excision of the lesion is the only real way to resolve symptoms and restore the nail.
X-ray revealing osteoid osteoma
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A less common cause of digit pain is an osteoid osteoma. This is a rare benign tumour of bone, which typically affects long bones such as the femur and tibia but 14 cases in the literature have been reported in the toes (5). The lesion has a gradual onset and grows to around 1 cm in the bone of the phalanx. The pain is typically worse at night but relieved by non-steroidal anti-inflammatory agents giving a clue to the aetiology. Lesions close to the surface may induce nail changes such as a yellow-brown discolouration, dystrophy and onychomadesis (6). Diagnosis is by X-ray which reveals the lesion. Surgical excision is the only effective treatment.
Summary
There are a number of causes of solitary painful nails, some of which have been covered here. Careful history taking and assessment can help to reach the correct diagnosis.
References
1 de Berker DAR, Wlodek C, Bristow IR. Subungual corn: a tender pigmented subungual lesion in older people. Br. J. Dermatol. 2014; 171: 69-72.
2 Sethu C, Sethu AU. Glomus tumour. Ann. R. Coll. Surg. Engl. 2016; 98: e1-e2.
3 Haenssle HA, Blum A, Hofmann-Wellenhof R et al. When all you have is a dermatoscope- start looking at the nails. Dermatology practical & conceptual 2014; 4: 11-20.
4 Fatih G, Güldehan A, Pembegül G et al. Subungual exostosis and subungual osteochondromas: a description of 25 cases. Int. J. Dermatol. 2018; 57: 872-81.
5 Xarchas KC, Kyriakopoulos G, Manthas S et al. Hallux Osteoid Osteoma: A Case Report and Literature Review. Open Orthop J 2017; 11: 1066-72.
6 Trave I, Chiarlone F, Barabino G et al. Osteoid osteoma of the great toe: dermatological signs as a disease spy. Int. J. Dermatol. 2020: early view.