Black discoloration of skin on right shoulder

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Black/Dark Discoloration of Skin on the Right Shoulder — Differential Diagnosis

Black or dark skin discoloration localized to the right shoulder has a fairly specific differential. Here are the most important causes to consider, organized by likelihood:

1. Notalgia Paresthetica (most classic for this location)

A sensory neuropathy caused by compression of dorsal rami of spinal nerves (typically T2–T6). It classically presents with hyperpigmentation on the right upper back at the medial scapular border/shoulder region, often accompanied by pruritus, burning, or tingling. The pigmentation results from chronic rubbing and scratching in response to the dysesthesia.

Cause: Degenerative cervicothoracic spine disease compressing nerve roots
Appearance: Well-demarcated, lichenified, hyperpigmented patch in the area of dysesthesia
Associated findings: Itch, burning, paresthesia
Management: Treat underlying spinal disease; topical capsaicin, gabapentin, or botulinum toxin for symptom relief; photoprotection

— Dermatology 2-Volume Set 5e

2. Becker Nevus

A unilateral acquired hyperpigmentation that classically begins as a tan-to-dark macule on the shoulder or pectoral area of a teenage male. Over time, hypertrichosis (increased hair) develops within the lesion.

Histology: Acanthosis, papillomatosis, increased basal cell pigmentation
Demographics: Most commonly adolescent males
Behavior: Benign; no malignant potential
Management: No treatment required; cosmetic options (laser) available if desired

— Andrews' Diseases of the Skin, Clinical Dermatology

3. Postinflammatory Hyperpigmentation (PIH)

Dark discoloration following any prior inflammatory skin condition (acne, eczema, contact dermatitis, trauma, infection). Very common cause of focal hyperpigmentation at any site.

Typically brown-to-dark brown; can appear black in darker skin phototypes
History of a preceding rash, injury, or infection at the site is key

4. Melanoma

Any irregularly pigmented dark/black lesion on the shoulder — especially with asymmetry, irregular borders, multiple colors, diameter >6 mm, or evolution — must raise concern for malignant melanoma.

The shoulder is a sun-exposed site and a common location for melanoma in men
ABCDE criteria: Asymmetry, Border irregularity, Color variation, Diameter >6mm, Evolution
Requires urgent dermatology referral and dermoscopy/biopsy

5. Tinea Nigra

A superficial fungal infection (Hortaea werneckii) causing brown-to-black pigmented macular patches, usually on the palms/soles but occasionally elsewhere.

Non-scaly, asymptomatic
KOH prep shows pigmented hyphae
Treated with topical antifungals

— Medical Microbiology 9e

6. Drug-Induced Hyperpigmentation

Certain drugs (amiodarone, minocycline, antimalarials, clofazimine) can cause blue-black discoloration in sun-exposed areas including the shoulders.

Clofazimine (used in leprosy): red to purple or black skin discoloration
Amiodarone: "muddy brown" pigmentation in sun-exposed areas

— Harrison's Principles of Internal Medicine 22E; Dermatology 2-Volume Set 5e

7. Metal Deposition (Black Dermographism)

Dark/black discoloration from deposition of metal particles (gold, silver, platinum) on skin — seen with jewelry or occupational exposure.

— Andrews' Diseases of the Skin

Key Clinical Questions to Narrow the Diagnosis

Feature	Points toward
Itching/burning at the site	Notalgia paresthetica
Teenage male, hairy patch	Becker nevus
Irregular, evolving, multicolored	Melanoma
Prior rash/trauma at the site	PIH
Long-term drug use	Drug-induced pigmentation
Jewelry/occupational metal exposure	Metal deposition

Any new, changing, or irregularly bordered dark lesion on the shoulder warrants dermatology evaluation and possible biopsy to exclude melanoma.

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