A patient is found to have a dark black lesion on the plantar surface of the foot. What is the most appropriate initial investigation?

Answer: C

Appeared in: INI-CET EXAM -2026

Explanation

A skin biopsy is the definitive diagnostic procedure for any skin lesion where malignancy is suspected.
The lesion shown in the image has characteristics highly suggestive of acral lentiginous melanoma (a type of skin cancer), including irregular borders, dark pigmentation, and ulceration.
Histopathological examination of the biopsy tissue is essential to confirm the diagnosis, determine the cancer's depth (Breslow thickness), and guide subsequent treatment planning.
As stated in dermatological practice, the diagnosis of melanoma is confirmed by an excision biopsy of the suspicious lesion.

Option A: A KOH (potassium hydroxide) mount is used to diagnose fungal infections by identifying fungal hyphae under a microscope.
Option B: A Gram stain is used to differentiate bacteria into Gram-positive and Gram-negative groups, guiding antibiotic therapy for infections.
Option D: A Tzanck smear is a cytological test used to find multinucleated giant cells, which are characteristic of infections with the herpes virus family (e.g., herpes simplex, varicella-zoster).

Clinical Relevance

Nursing practice connection: Use the key finding related to Diagnostic evaluation of suspicious skin lesions to guide bedside assessment, documentation, and the next nursing action.
Nurses are often the first healthcare professionals to perform a skin assessment and can play a vital role in the early detection of skin cancers by recognizing suspicious lesions.
Acral lentiginous melanoma, which occurs on the palms, soles, and under the nails, is more common in individuals with darker skin tones and can be diagnosed late due to its location. This underscores the importance of thorough foot examinations, especially in high-risk populations like patients with diabetes.
Promptly reporting suspicious skin findings and advocating for a dermatological referral and potential biopsy can significantly improve patient outcomes, as the prognosis for melanoma is strongly linked to the stage at diagnosis.

How to Approach the Question

First, carefully analyze the image provided. Note the key characteristics of the lesion: its location (plantar surface of the foot), color (dark black), borders (irregular), and surface (ulcerated).
Recognize that these features are 'red flags' or warning signs for malignant melanoma.
Read the question, which asks for the 'most appropriate initial investigation' to establish a diagnosis.
Evaluate each option based on its primary diagnostic purpose. A KOH mount is for fungi, a Gram stain for bacteria, a Tzanck smear for viruses, and a skin biopsy for tissue analysis (cancer).
Connect the clinical presentation to the appropriate test. Since the primary suspicion is cancer, a tissue diagnosis is required.
Conclude that a skin biopsy is the only option that can definitively diagnose or rule out melanoma, making it the most appropriate choice.

Concept Tested & Keywords

Concept Tested: Diagnostic evaluation of suspicious skin lesions
Stem keywords: dark black lesion, plantar surface, foot, initial investigation
Lead-in keywords: most appropriate
Clinical cues: The image of a large, dark, ulcerated lesion on the foot is a significant clinical cue suggesting malignancy, specifically melanoma.

QWVIKojj1r3g7qZGwueVY6

E6 Nelson Textbook of Pediatrics(2024) — Volume 2 p. 1835-1837

E6 Nursing Brunner Adult Health 3SA Vol 1 Part 4 p. 61-63

E6 Medicine Davidson Principles Practice 24e p. 1253-1255

Practise the full INI-CET EXAM -2026

Attempt every question from this paper in a timed mock, then review the full solution for each one.