Differential Diagnosis for Melanychia with Pain and Microcytic Anemia
- Single most likely diagnosis:
- Iron deficiency anemia: The patient's microcytic anemia and melanychia (likely melonychia, which is a discoloration of the nails) could be related to iron deficiency, which is further supported by the patient's habit of biting their nails (onychophagia), a common sign of iron deficiency.
- Other Likely diagnoses:
- Trauma or repetitive strain injury: The pain with finger extension at the MCPJ into PIPJ and finger flexion could be due to trauma or repetitive strain, especially if the patient bites their nails aggressively, causing micro-trauma to the nail bed and surrounding tissues.
- Psoriatic arthritis: Although less common, psoriatic arthritis could cause pain and swelling in the fingers, as well as nail changes like melonychia, and is sometimes associated with iron deficiency anemia.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.):
- Subungual melanoma: Although rare, subungual melanoma can present with melonychia and should be considered, especially if the discoloration is isolated to one nail or if there are other suspicious features like a changing mole or unexplained pain.
- Sickle cell disease: This condition can cause microcytic anemia and may lead to nail changes, including melonychia, due to vaso-occlusive crises affecting the nail bed.
- Rare diagnoses:
- Hemochromatosis: A genetic disorder leading to iron overload, which can cause skin and nail changes, but typically presents with macrocytic anemia rather than microcytic anemia.
- Sjögren's syndrome: An autoimmune disorder that can cause dryness and inflammation in various parts of the body, including the nails, but is less commonly associated with melonychia and microcytic anemia.