A 76-year-old man presented with areas of progressive skin darkening for 2 years. On exam, he had hyper-pigmented, non-blanching coalescent macules on his arms, legs, and abdomen (Figs. 1 and 2). They were painless and non-pruritic. He had been taking minocycline as suppressive therapy for an infection that complicated a C3–C7 laminectomy and posterior fusion 27 months earlier. He was diagnosed with minocycline-induced hyperpigmentation (MIH).

Figure 1
figure 1

Hyperpigmented macules on the lower extremities.

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Figure 2
figure 2

Hyperpigmented macules on the upper extremities.

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The differential diagnosis for acquired hyperpigmentation includes melasma, pigmented contact dermatitis, drug-induced hyperpigmentation (DIH), erythema dyschromicum perstans, Addison’s disease, hyperthyroidism, hemochromatosis, and cutaneous malignancies. These disorders generally result from increased melanin, increased melanocytes, or deposition of another discoloring substance in the skin.1 Medications commonly cited as causing hyperpigmentation include prostaglandins, minocycline, phenothiazine, nicotine, and antimalarial drugs.2 MIH typically occurs in a dose-dependent fashion after large cumulative doses of 70–100 g, but may appear within weeks of starting the medication.3 In one study, 17 % of patients taking minocycline developed hyperpigmentation.4 In addition to the skin, MIH can involve the sclera, nails, ear cartilage, bone, oral mucosa, teeth, and thyroid gland.5 Therapy for MIH is cessation of the medication, after which the discoloration may slowly improve. If discoloration persists, laser therapy may also be used.5