sarcoid
Meaning of sarcoid: Granulomas of sarcoid look almost identical to those of tuberculosis under the microscope, so infection has to be excluded before the label is applied.
Definition of sarcoid
Sarcoid is the shortened name for sarcoidosis, an inflammatory disease in which immune cells clump together into small nodules called granulomas. The lungs and the lymph nodes inside the chest are affected most often, but the skin, eyes, liver, nerves and heart can be involved as well. No infection or single trigger has been identified as the cause.
What does a sarcoid granuloma look like?
A granuloma is a tight ball of immune cells, mainly macrophages that have fused into large multinucleated forms, ringed by lymphocytes. In sarcoid these are non-caseating, meaning the center stays solid rather than breaking down into the soft, cheese-like debris seen in tuberculosis. That single feature is the most useful pathological clue, though it is not proof on its own. The immune reaction behaves as though it is answering an antigen that no one has yet been able to identify, and it is disordered rather than absent, which is why an infection is not the explanation.
Which organs does it involve?
| Site | What appears |
|---|---|
| Chest lymph nodes and lungs | Involved in the large majority of cases; cough, breathlessness, or nothing at all |
| Skin | Raised violet patches, nodules, or tender red bumps on the shins |
| Eyes | Inflammation inside the eye, which can be silent early on |
| Heart and nervous system | Uncommon but disproportionately serious, causing rhythm disturbance or nerve palsies |
| Liver, spleen, joints, kidneys | Often found incidentally on scans or blood tests |
How is it recognized?
Diagnosis rests on three legs at once: a compatible clinical picture, granulomas without caseation on a tissue biopsy, and the exclusion of other causes. Chest imaging showing symmetrically enlarged lymph nodes at both lung roots is a strong pointer. Blood tests may show a raised calcium level, because granuloma cells activate vitamin D, and a raised angiotensin-converting enzyme level, which supports the picture but is far too unreliable to stand alone. Because tuberculosis, fungal disease and reactions to metal dusts all produce granulomas, tissue is cultured and stained before inflammation is attributed to sarcoid.
Used in a sentence
A lymph node biopsy showed granulomas consistent with sarcoid.
Good to know
Sarcoid granulomas resemble those seen in certain infections, such as tuberculosis, so infectious causes are typically ruled out before a diagnosis of sarcoid is confirmed.
Word origin
Where “sarcoid” comes from
Formed from sarc-, from Greek sarx, sarkos, meaning flesh, combined with -oid, meaning resembling.