What’s your diagnosis? This is not lingua nigra. It has some kind of environmental cause. I’ll post the correct a answer in about three days!
Is this patient taking chemotherapy for any malignancy? if so this can be a chemotherapy-Induced hyper-pigmentation of his tongue
Correct answer: Chemotherapy-induced hyperpigmentation of the tongue. A common side-effect of chemotherapy, especially when using doxorubicin or cyclophosphamide. It should resolve spontaneously in about 12 weeks.