diff --git a/atlas/forms.py b/atlas/forms.py
index fd0041bf..2d80f167 100755
--- a/atlas/forms.py
+++ b/atlas/forms.py
@@ -1033,6 +1033,37 @@ class ConditionAutocomplete(ModelAutocomplete):
     model = Condition
     search_attrs = ["name"]
 
+    @classmethod
+    def get_items_from_keys(cls, keys, context_obj=None):
+        """Return items for given keys, ignoring empty strings.
+
+        The autocomplete frontend sometimes sends empty string keys which
+        causes the ORM to raise ValueError when filtering numeric PK fields.
+        Filter out falsy/blank keys before querying. If no valid keys remain
+        return an empty queryset.
+        """
+        # normalize and remove empty/blank values
+        clean_keys = [k for k in keys if k is not None and str(k).strip() != ""]
+        if not clean_keys:
+            return cls.model.objects.none()
+
+        # try to convert numeric keys to ints where possible
+        parsed_keys = []
+        for k in clean_keys:
+            try:
+                parsed_keys.append(int(k))
+            except Exception:
+                parsed_keys.append(k)
+
+        qs = cls.model.objects.filter(pk__in=parsed_keys)
+
+        # Return a list of dicts matching the autocomplete core expectations
+        # (items subscriptable by keys like 'key' / 'label').
+        return [
+            {"key": obj.pk, "label": getattr(obj, "name", str(obj)), "value": str(obj)}
+            for obj in qs
+        ]
+
 
 class ConditionAutocompleteForm(Form):
     condition = ModelChoiceField(
diff --git a/atlas/templates/atlas/condition_detail.html b/atlas/templates/atlas/condition_detail.html
index d48e1f56..b56332d3 100755
--- a/atlas/templates/atlas/condition_detail.html
+++ b/atlas/templates/atlas/condition_detail.html
@@ -36,6 +36,28 @@
                             {% empty %}
                                 —
                             {% endfor %}
+                            {% if request.user.is_authenticated and can_merge %}
+                                <div class="mt-2">
+                                    <a class="btn btn-sm btn-outline-primary" data-bs-toggle="collapse" href="#addSynonymCollapse" role="button" aria-expanded="false" aria-controls="addSynonymCollapse">Add synonym</a>
+                                </div>
+                                <div class="collapse mt-2" id="addSynonymCollapse">
+                                    <div class="card card-body">
+                                        <form method="POST">
+                                            {% csrf_token %}
+                                            <input type="hidden" name="action" value="add_synonym" />
+                                            <div class="mb-2">
+                                                <label class="form-label small">Select existing condition</label>
+                                                {{ synonym_form.condition }}
+                                            </div>
+                                            <div class="mb-2">
+                                                <label class="form-label small">Or create new synonym name</label>
+                                                <input class="form-control" type="text" name="synonym_name" placeholder="e.g. Granulomatosis with Polyangiitis" />
+                                            </div>
+                                            <button class="btn btn-primary btn-sm" type="submit">Add</button>
+                                        </form>
+                                    </div>
+                                </div>
+                            {% endif %}
                         </dd>
 
                         <dt class="col-sm-4">Parent</dt>
diff --git a/atlas/views.py b/atlas/views.py
index fad32331..9f92498c 100755
--- a/atlas/views.py
+++ b/atlas/views.py
@@ -830,7 +830,12 @@ def question_schema_schemas(request):
 def condition_detail(request, pk):
     condition = get_object_or_404(Condition, pk=pk)
 
-    form = ConditionAutocompleteForm()
+    # form used for the merge UI
+    merge_form = ConditionAutocompleteForm()
+
+    # form used to add a synonym (can post either an existing condition via autocomplete
+    # or provide a plain name in 'synonym_name')
+    synonym_form = ConditionAutocompleteForm()
 
     can_merge = False
 
@@ -840,11 +845,47 @@ def condition_detail(request, pk):
     ):
         can_merge = True
 
+    # Handle POST to add a synonym
+    if request.method == "POST" and request.POST.get("action") == "add_synonym":
+        # only allow staff/editors
+        if not (
+            request.user.is_superuser
+            or request.user.groups.filter(name="atlas_editor").exists()
+        ):
+            return HttpResponse("Forbidden", status=403)
+
+        # Try autocomplete-selected condition first
+        form = ConditionAutocompleteForm(request.POST)
+        other = None
+        if form.is_valid():
+            other = form.cleaned_data.get("condition")
+
+        # If no autocomplete selection, accept a free-text name
+        synonym_name = request.POST.get("synonym_name")
+        if not other and synonym_name:
+            other, created = Condition.objects.get_or_create(name=synonym_name)
+            if created:
+                # mark created synonym as non-primary
+                other.primary = False
+                other.save()
+
+        if other and other != condition:
+            # add mutual synonym relationship
+            condition.synonym.add(other)
+            other.synonym.add(condition)
+
+        return redirect("atlas:condition_detail", pk=condition.pk)
+
     # logging.debug(atlas.subspecialty.first().name.all())
     return render(
         request,
         "atlas/condition_detail.html",
-        {"condition": condition, "form": form, "can_merge": can_merge},
+        {
+            "condition": condition,
+            "form": merge_form,
+            "synonym_form": synonym_form,
+            "can_merge": can_merge,
+        },
     )