When A Discolored Toenail Suggests A More Concerning Diagnosis

A 34-year-old female presented to our institution with the chief complaint of a painful, dystrophic and discolored nail plate on her left hallux. This complaint began approximately five years ago when she had a total nail avulsion without a matrixectomy. She stated that when the nail grew back, it grew back thicker.

The patient also noted there was an area of the nail bed that had black discoloration. The provider at that time did not perform a biopsy. As the nail grew back, the nail plate continued to appear abnormal in shape and thickness. She complained of a dull ache and sometimes throbbing pain to the distal medial portion of the nail fold, which was worse with pressure or closed toe shoes. Since childhood, the patient had a flesh-colored skin growth along the medial nail fold, which she insisted had remained the same size and shape. She said the skin growth had never ulcerated, changed in color or consistency, and had never been painful. The patient assumed it was fungus or a skin tag.

She did not notice purulent drainage around the nail or nail fold. The patient denied any constitutional symptoms. She stated that the medial portion of the nail plate had become slightly black over the past year or so, and that she was applying an antifungal ointment (that she had bought in Mexico) to the nail plate. The topical medication had not improved the discoloration of the nail plate.
Her past medical history was unremarkable. Her surgical history was significant for a caesarean section and tubal ligation. The patient had no known drug allergies. Her social habits were unremarkable. She was married with two children.

Key Questions To Consider

1. What are the key characteristics of this condition?
2. What is the differential diagnosis?
3. What factors made the differential diagnosis challenging?
4. What is the correct diagnosis?
5. What is the appropriate treatment?

Answering The Key Diagnostic Questions
1. The left hallux nail plate had a thickened appearance with discoloration and dystrophy. An area with subungual debris was present along the medial hyponychium. The most medial one-fifth of the nail plate had a black, discolored appearance without any mass under the nail plate.
2. Seborrheic keratosis, lentigo, melanoma, periungual fibroma or melanocytic nevus
3. There were many points of concern, such as pigmented skin and nail lesion, a flesh-colored nodular lesion, and an element of pain.
4. Acral lentiginous melanoma
5. Partial amputation of the great toe

A Closer Look At The Patient Presentation
The physical exam revealed a well-dressed, well-nourished female with a normal body habitus. The vascular exam revealed strong palpable pulses. Capillary refill was immediate to the level of the digits. The neurologic exam revealed symmetric and equal deep tendon reflexes, and there was no loss of epicritic sensation. The orthopedic exam revealed symmetric, pain-free range of motion of the left great toe at the interphalangeal joint and metatarsophalangeal joint levels.

The dermatologic exam revealed a left hallux nail plate with a thickened appearance, discoloration and dystrophy. There was an area of subungual debris visible along the medial hyponychium. The most medial one-fifth of the nail plate had a black, discolored appearance without any mass under the nail plate (see photo above at left). The skin folds did not have a black, necrotic appearance and there was a negative Hutchinson’s sign. The nail plate appeared to be intact to the underlying nail bed. There was a nodular lesion with a flesh-colored skin growth that was serpentine in shape and smooth in texture along the medial aspect of the proximal nail. Web spaces were clean and dry without maceration. There was no clinical sign of infection. There were no hyperkeratotic skin lesions on the patient’s feet.

The patient elected to have the nail removed. After nail removal, the features of the left hallux nail were thickened, discolored and dystrophic with subungual debris. The medial portion of nail plate was hyperpigmented, black and incurvated with evidence of nail spicules. There was an area of pigmented nail bed in the proximal medial corner of the hallux (see photo at the right).

Why The Differential Diagnosis Was Difficult
The differential diagnoses for this case were challenging due to the fact that there were many elements of concern. There was a pigmented skin and nail lesion, a flesh-colored nodular lesion, and an element of pain. Certainly, there can be multiple problems affecting her toe. Differential diagnoses would have to include a nail disease condition of onychomycosis, onychodystrophy and/or subungual hematoma. A pigmented skin lesion would include differential diagnoses of melanoma, nevus, seborrheic keratosis and lentigo. A non-pigmented nodular lesion may include differential diagnoses of fibroma, skin tag and intradermal nevus.

Common nail disease includes onychomycosis and traumatic nail dystrophy. Discoloration of the nail plate is usually old subungual hematoma. When the darkened area of the nail plate does not “grow out” with the nail, there should be a high index of suspicion for a pigmented skin lesion on the nail bed. One should remove the nail plate and biopsy any pigmented skin lesion. Typically, there is no pain associated with a dark colored nail. If the nail border is causing pain that typically occurs with onychocryptosis, then there is usually an inflamed nail border with minor signs of infection and/or pyogenic granuloma.

Seborrheic keratosis is a benign pigmented skin lesion. The lesions may be tan, brown or black. They may have a waxy or fine scaling appearance, and can be raised or flat. These lesions are common in older adults and typically affect the face, chest, shoulder and back. These lesions never become cancerous.

A lentigo is a pigmented skin lesion that can vary from tan to black in color. Lentigines can appear anywhere on the body and typically have a clearly defined sharp border. The most common form of lentigo is not due to sun damage but rather is identified at birth or in early childhood. Solar lentigines, on the other hand, are secondary to sun damage on the skin and are commonly referred to as “age spots or liver spots” arising typically on the face, arms and hands.

Melanoma is the most feared skin cancer due to the potential for metastasis and death. The five main subtypes of melanoma include superficial spreading, nodular, lentigo maligna, acral lentiginous and amelanotic melanoma. Acral lentiginous melanomas are typically the most common type of melanomas found in the nail bed. Amelanotic melanoma can be challenging to diagnose due to the lack of pigmentation.

A periungual fibroma is an uncommon benign nodular skin lesion. These lesions may be associated with tuberous sclerosis or Von Recklinghausen’s disease. These lesions may place pressure on the nail matrix or nail fold, causing pain.

Skin tags are fibroepithelial polyps, which are typically visible on the face and neck and areas where there is skin to skin contact such as the armpit and groin. These are benign growths that rarely change in size. A typical lesion is the size of a rice grain. Skin tags can get irritated with the friction of clothes or rubbing.

A melanocytic nevus is characterized by increased proliferation of melanocytes in the skin. Depending on the level of melanin deposition, the color of these lesions may vary. For example, if increased melanocytes are in the stratum corneum layer, then the lesion may be black. If the melanocytes are deeper in the reticular dermis, then the lesion may be gray or blue in color. The appearance of a nevus can vary to include lesions that are flat, elevated, sessile, smooth or rough. The “ABCD” rule comes into play when differentiating a nevus from melanoma. Nevi should have a symmetric shape, regular border, uniform color and small size (diameter <6 mm). If those findings are contrary to the lesion in question, then a biopsy is in order to rule out melanoma.

Pertinent Insights On The Diagnosis And Treatment
In this case, a biopsy was necessary to make the diagnosis. For the sake of completeness, a radiograph of the left foot revealed no osseous abnormalities and magnetic resonance imaging (MRI) with and without IV contrast revealed a small soft tissue defect along the dorsal aspect of the first digit distally without an associated enhancement of the underlying mass. We ultimately obtained a 4 mm punch biopsy from the proximal medial aspect of the left hallux, including a portion of the nail bed, which was hyperpigmented, as well as the flesh-colored skin lesion at the level of the eponychium. Pathological examination revealed a Clark’s level IV melanoma with a thickness of 1.98 mm. This was consistent with an acral lentiginous melanoma.

Definitive treatment for this patient included a partial amputation of the great toe. At the same time the melanoma surgery took place, a sentinel lymph node biopsy was positive.

We then referred the patient for computed tomography (CT) images of her chest, abdomen and pelvis along with a chest radiograph to evaluate for distant metastasis, which were all negative.

The patient has been discharged from the podiatry service with a healed surgical site. She has had close follow-up with the hematology/oncology department of our institution for ongoing medical observation and treatment.

In Summary
This case stresses the importance of taking a biopsy from any suspicious looking skin lesion. In this case, an acral lentiginous melanoma was present and the main concern of the patient was a discolored nail plate with mild pain. There is very little medical risk to the patient by taking a biopsy. Missing the diagnosis, however, can have ominous implications.

Dr. Tehrani is a third-year resident at Maricopa Medical Center in Phoenix.

Dr. Lardizabal is a third-year resident at Maricopa Medical Center in Phoenix.

Dr. Fishco is board-certified in foot surgery and reconstructive rearfoot and ankle surgery by the American Board of Podiatric Surgery. He is a Fellow of the American College of Foot and Ankle Surgeons, and a faculty member of the Podiatry Institute. Dr. Fishco is in private practice in Phoenix.